Soften the squash: Microwave the whole spaghetti squash for about 5 minutes, then let it cool slightly. Cut in half lengthwise and remove the seeds.
Roast: Place squash halves cut-side down on a baking sheet. Roast at 425°F until fork-tender and the strands pull away easily, about 30–45 minutes. Scrape out the strands and set aside.
Make the sauce: Heat a drizzle of avocado oil in a skillet over medium heat. Add the tomatoes and onion and cook until the tomatoes begin to burst and the onion softens.
Finish: Lower the heat and add the heavy cream, parmesan, and spaghetti squash strands. Toss gently until combined and warmed through and the sauce has thickened slightly. Remove from heat, add lemon juice and zest, and season with kosher salt and fresh ground pepper to taste.
Notes
The longer you microwave the squash, the less time required in the oven.Add extra parmesan. Because you can. And, you should.