Adjust rack to top position and preheat oven to 450 degrees. Bring a medium pot of salted water to a boil. Wash and dry all produce. Halve, peel, and dice half the onion (whole onion for 4 servings). Finely dice tomato. Trim zucchini, then grate on the largest holes of a box grater.

Once water is boiling, add penne to pot. Cook until almost al dente, 8 minutes (it’ll cook more in step 6). Drain. Keep empty pot handy for step 5.

Meanwhile, heat a drizzle of olive oil in a large pan over medium-high heat. Add diced onion, tomato, and a pinch of salt. Cook, stirring occasionally, until onion is softened, 4-6 minutes. Stir in marinara, zucchini, half the Italian Seasoning, ¼ cup water (½ cup for 4 servings), 1 tsp sugar (2 tsp for 4), and a big pinch of salt. Bring to a simmer. Cook, stirring, 3 minutes more; turn off heat.

While sauce simmers, in a medium bowl, combine ricotta, remaining Italian Seasoning, and a drizzle of olive oil. Season with salt and pepper.

Add penne, sauce, and 1 TBSP butter (2 TBSP for 4 servings) to pot used for pasta. Season with salt and pepper; stir to thoroughly combine. Spread out half the pasta mixture in an 8-by-8-inch baking dish. (For 4 servings, use a 9-by13-inch baking dish.) Using a tablespoon, dollop pasta mixture with herbed ricotta. Top with remaining pasta mixture, then sprinkle with mozzarella.

Cover baking dish with foil. (TIP: Coat inside of foil with nonstick spray first to prevent sticking.) Bake pasta on top rack for 10 minutes, then remove from oven; discard foil. Heat broiler to high. Broil on top rack until cheese is lightly browned, 4-5 minutes. Let cool slightly; top with chili flakes if desired. Divide between plates and serve.