Easy Keto Spaghetti Sauce

⏲ ~50 min total · prep 15 · cook 35 · 4 servings

By the KFI Test Kitchen · Tested & approved by Jason Lieu, KFI recipe editor

Published Sep 15, 2026 · Updated Sep 15, 2026

Ingredients

• 3 tbsp olive oil
• 4 cloves garlic, thinly sliced
• 2 tbsp tomato paste
• 1 (28 oz) can crushed tomatoes
• 1 tsp dried oregano
• 1/2 tsp red pepper flakes
• 1 tsp kosher salt
• 1/4 cup grated Parmesan
• 1/4 cup fresh basil leaves, torn
• 2 medium zucchini, spiralized

Instructions

1. Warm the olive oil and garlic slices in a wide 3-quart sauté pan over medium-low heat for 2 minutes, until the garlic is fragrant and barely golden — never browned, or the whole sauce turns bitter.
2. Add the tomato paste and fry it, stirring constantly, for 1 minute until it darkens a shade and smells sweet.
3. Pour in the crushed tomatoes, then swirl 1/4 cup water in the empty can to catch the last of the pulp and add that too.
4. Stir in the oregano, red pepper flakes, and salt, bring to a lively simmer, and cook uncovered 10 minutes, stirring now and then, until the sauce deepens from bright red to brick red and pools slowly off a spoon.
5. Pull the pan off the heat and stir in the Parmesan and torn basil until the cheese melts into the sauce.
6. Toss with the spiralized zucchini in the warm pan for just 30 seconds — long enough to coat and take the raw edge off the noodles without weeping water — and serve immediately.

Why this recipe works

• Fried tomato paste One minute of frying in hot oil darkens the paste and builds a sweet, roasted depth a ten-minute sauce cannot reach on its own. It is the whole reason this tastes longer-cooked than it is.
• Sliced garlic Thin slices take two minutes of gentle heat without scorching. Minced garlic browns in spots over the same flame and drags the whole sauce bitter.
• Zucchini at the end Spiralized zucchini needs 30 seconds in the warm pan and nothing more. Coated and barely warmed, it holds its shape instead of weeping water into the sauce.

Tips for making this recipe well

Guard the garlic

Medium-low heat and two minutes is all it gets. Past barely golden, the bitterness follows the sauce to the table. Pull it early if you are unsure; the paste stage rescues pale garlic.

Swirl the can

A quarter cup of water swirled in the empty can catches the pulp stuck to the sides. It thins the sauce to a spooning consistency and wastes nothing.

Cook to brick red

Ten uncovered minutes at a lively simmer turns crushed tomatoes from bright red to brick. The sauce should pool slowly off a spoon. If it still runs, keep it going two minutes more.

Cheese and basil off the heat

Stir the Parmesan and torn basil in after the pan leaves the burner, so the cheese melts creamy instead of stringy. The basil keeps its color against the red.

Thirty seconds for the noodles

Toss the spiralized zucchini in the warm pan, coat, and plate. Any longer and the noodles soften and release water that pools under the sauce. Serve immediately, with extra Parmesan at the table.

Serving suggestions

Fifteen minutes, one pan, and dinner is handled. Serve the sauce over the zucchini noodles the moment they are tossed, because the noodles are at their best in the first few minutes. Put extra Parmesan and torn basil on the table and let people finish their own bowls. At 3.6 net carbs a serving, the sauce leaves room for meatballs or grilled chicken on the nights you want more on the plate.

Storage and meal prep

The sauce is the keeper here. Refrigerate it covered for three to four days, or freeze it for two to three months; it is tomatoes, oil, and cheese, and it freezes clean. Keep the sauce separate from the zucchini noodles, which turn limp and watery by the next day. When you reheat, spiralize fresh zucchini, warm the sauce, and toss in the pan for 30 seconds as written.

Variations worth trying

• Earlier heat Add the red pepper flakes to the oil with the garlic instead of with the tomatoes. Blooming them first spreads the warmth through the whole pan.
• Sausage version Brown crumbled Italian sausage in the pan first and build the sauce on the rendered fat, cutting the olive oil to a tablespoon. Dinner gets a protein and the sauce gets depth.
• Pink sauce Stir a quarter cup of heavy cream in with the Parmesan for a rosé version. The tomato softens and the sauce clings harder to the noodles.
• Dairy-free Skip the Parmesan and finish with an extra tablespoon of olive oil and a bigger pinch of salt. Tomato paste and basil carry the sauce on their own.

Frequently asked questions

Why did my garlic turn bitter?

It browned. Thin slices go from fragrant and barely golden to burnt in well under a minute over anything hotter than medium-low. Start over with fresh oil if yours went dark, because the bitterness does not wash out.

Can I use fresh tomatoes?

Not in fifteen minutes. Fresh tomatoes need a long cook to break down and concentrate, which is what this recipe is built to skip. Canned crushed tomatoes give the same texture every weeknight.

How do I stop zucchini noodles from turning watery?

Toss them in the warm pan for 30 seconds and serve right away. Salting ahead, or burying them under sauce, pulls water out and pools it in the bowl. A short toss and fast plating is the whole trick.

Can I make the sauce ahead?

Yes, and it improves overnight in the fridge. It keeps three to four days refrigerated or two to three months frozen. Thaw, reheat, and toss with fresh noodles for a five-minute dinner.

Is this sauce spicy?

A half teaspoon of red pepper flakes gives background warmth rather than real heat. Halve them for sensitive palates or skip them entirely. The sauce stands on garlic and tomato paste without the chile.

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