Toss together the cherry tomatoes, chopped onion, garlic, red pepper flakes and olive oil. Spread in a single layer on a baking sheet and roast for 30 minutes until vegetables have softened and tomatoes have slightly burst.
While the vegetables are cooking, bring a large pot of salted water (use the 3/4 teaspoon salt) to a boil. Add the ziti and cook until tender according to package directions; drain, reserving 1 cup pasta water.
Add the cooked tomato mixture, cashews and 3/4 cup reserved pasta water to a high powered blender and puree until very creamy. Depending on the power of your blender, this may take ~5 minutes. Taste, adding more salt/red pepper flakes/black pepper as needed.
Toss the hot pasta with the creamy tomato sauce and the torn basil leaves. Serve immediately!
Notes
I photographed this with leftover crumbled tempeh bacon that I had on hand. You can use this tempeh bacon recipe or purchase it if you want an extra protein boost!