Preheat the oven and prep the dish: Heat your oven to 375°F (190°C). Lightly spray a 9x13-inch baking dish with nonstick spray.
Brown the sausage: Heat a large skillet over medium heat. Add olive oil if needed, then turkey sausage.
Cook, breaking it up with a spoon, until browned and cooked through, about 6–8 minutes.
Sauté the aromatics: Add the diced onion to the skillet. Cook until softened, about 3–4 minutes. Stir in garlic and cook 30 seconds until fragrant.
Build the sauce: Pour in marinara and the crushed or diced tomatoes if using.
Stir in Italian seasoning, red pepper flakes, and a pinch of salt and pepper. Simmer 3–5 minutes to meld flavors.
Add the greens: Stir in the chopped spinach. Cook 1–2 minutes until just wilted.
Taste and adjust seasoning.
Combine with tortellini: Add the refrigerated tortellini directly to the skillet. Stir to coat. No need to pre-boil; it will finish cooking in the oven.
Layer in the dish: Spoon half of the sauced tortellini into the baking dish.
Dollop half the ricotta in small spoonfuls. Add a light sprinkle of mozzarella and Parmesan. Repeat with remaining tortellini, the rest of the ricotta, and a final sprinkle of cheeses.
Bake: Cover loosely with foil and bake for 15 minutes.
Remove foil and bake another 10–12 minutes, until bubbly and the cheese is melted with lightly golden spots.
Rest and garnish: Let it rest 5 minutes. Sprinkle with chopped basil or parsley. Serve warm.