Preheat oven to 300 degrees F (148 C). Line a baking sheet with parchment paper. Slice tomatoes in half lengthwise and toss with a little oil and sea salt. Arrange the tomatoes cut-side up and place on the center rack of your oven. Bake for 30-40 minutes, or until the edges have shriveled and the tomatoes have shrunken slightly.
In the meantime, prepare sauce by soaking raw cashews in very hot water for 30 minutes.
Once the cashews are almost done soaking, bring a pot of water to a boil and season with a healthy pinch of salt. Once boiling, add pasta and cook according to package instructions. Drain and set aside until serving (ideally the pasta is ready within a few minutes of serving — try to time accordingly).
After the 30 minutes are up, drain and rinse cashews and add to a small blender. Add remaining sauce ingredients (garlic, nutritional yeast, salt, and water or almond milk — we used half water, half almond milk) and blend until creamy and smooth. The sauce should be thin and pourable (add more water as needed).
Taste and adjust flavors as needed, adding more nutritional yeast for cheesiness, salt to taste, or garlic for zing. Set aside.
Once your sauce is ready, the tomatoes are nearly done roasting, and the pasta is almost ready, heat a large skillet over medium heat. Once hot, add a small amount of oil to coat pan (if oil-free, use water) and add sliced onion and yellow squash. Season with salt and pepper, Italian seasonings (optional) and a pinch of red pepper flakes (optional). Ensure the squash is in a single layer and not overlapping so it gets evenly cooked.
Once browned on the underside, use tongs or a spatula to flip the squash and cook on the other side for 3-4 minutes more. Once onion and squash are tender and slightly brown, add spinach (or other greens of choice), and stir to combine. Season with another pinch salt and pepper.
Add cooked drained pasta to the pan and pour over the sauce. Toss to combine. Lastly, add the roasted tomatoes and stir.
Serve immediately as is, or garnish with fresh herbs (such as parsley or basil), vegan parmesan cheese, or red pepper flake (all optional). Store leftovers covered in the refrigerator up to 3-4 days (reheat in the microwave or on the stovetop until hot, adding a little dairy-free milk if it appears dry). Not freezer friendly.
*Nutrition information is a rough estimate calculated with avocado oil and water instead of almond milk, and without optional ingredients.