Preheat oven to 425 F.
Grind mushrooms in a food processor. Transfer to a large, dry skillet, sprinkle with a dash of salt (optional), and sauté mushrooms on medium-high for 3 to 5 minutes to remove some of the moisture. Set aside and let cool.
In a large bowl, thoroughly mix mushrooms, sweet potato, ground turkey, Italian seasoning, garlic powder, salt, bread crumbs, Parmesan cheese, and egg. Create 20 to 25 1½-inch meatballs; space evenly on a baking sheet with edges and bake until fully cooked through, about 20 minutes.
In a food processor, purée spinach and cauliflower. Steam in large skillet with a few tablespoons of water for about 5 minutes. Add pasta sauce and meatballs to skillet; stir and cook until heated through.
Top pasta with meatballs and sauce. Serve sprinkled with cheese, if desired.
If you’re not so sure about hiding vegetables in both the meatballs and the sauce, try out one at a time. Meatballs can be made ahead in batches and frozen for up to 3 months.
Per serving: 548 calories, 16 grams fat (3.5 grams saturated fat), 153 milligrams cholesterol, 1,050 milligrams sodium, 68 grams total carbohydrates, 7 grams fiber, 36 grams protein.