Begin by preparing the vegetable-based pasta sauce. In a wide, deep skillet set over medium heat, warm the olive oil. Add the chopped onion and sauté for 3 to 5 minutes, stirring occasionally, until softened and lightly golden.

Add the zucchini, yellow squash, minced garlic, dried oregano, red pepper flakes, and a generous pinch of salt. Cook for 5 to 8 minutes, stirring occasionally, until the vegetables are tender yet still retain a bit of bite.

Stir in the tomato paste and cook for an additional minute to deepen the flavor. Then add the roasted red peppers, whole peeled tomatoes, and mushroom powder, if using. Bring the mixture to a gentle simmer and let it cook for approximately 10 minutes. As the sauce thickens and reduces, use a spoon or spatula to break up the tomatoes into rustic chunks for a hearty texture.

While the sauce is simmering, bring a large pot of salted water to a rolling boil. Cook the spaghetti according to package instructions until al dente. Drain the pasta and set it aside.

Remove the sauce from the heat and stir in the fresh spinach and torn basil leaves. The residual heat will wilt the spinach and allow the herbs to release their aroma. Taste the sauce and adjust the seasoning with additional salt or pepper if needed.

Add the cooked pasta to the sauce and let it rest for a minute, allowing the noodles to absorb the flavors and the spinach to soften further. Toss everything together gently to coat the pasta thoroughly in the sauce.

Serve immediately, garnished with additional fresh basil and a generous sprinkle of parmesan cheese or nutritional yeast, depending on your preference.