Heat oven to 375°F. Lightly oil a 9x13-inch baking dish.
Boil ziti in salted water until just shy of al dente. Reserve 1/2 cup cooking water, then drain.
Warm olive oil in a skillet over medium heat. Soften onion for 5 minutes.
Stir in garlic and cook 30 seconds. Add marinara, Italian seasoning, red pepper, salt, and black pepper.
Simmer sauce 5 minutes. Fold in spinach to wilt. Stir in half the basil.
Combine ricotta with 1 cup mozzarella and 1/4 cup Parmesan in a bowl until creamy.
Toss cooked ziti with the sauce. Splash in reserved pasta water to loosen and coat.
Spread a thin layer of sauced ziti in the dish. Dollop half the ricotta mix over it.
Add half of the remaining ziti. Sprinkle with 1 cup mozzarella and 1/4 cup Parmesan.
Repeat layers with remaining ziti and ricotta. Finish with the rest of mozzarella and Parmesan.
Cover with foil and bake 20 minutes. Uncover and bake 8–10 minutes until bubbly and lightly browned.
Rest 10 minutes. Scatter remaining basil and serve warm.
Notes
Variation: Stir in sautéed mushrooms or swap spinach for chopped kale. For extra heat, add more red pepper flakes. Storage: Refrigerate leftovers up to 4 days or freeze up to 2 months. Reheat covered at 350°F until hot.This recipe is an original creation inspired by classic Easy Meatless Baked Ziti Recipe flavors. All ingredient ratios and instructions are independently developed.