To cook immediately, preheat the oven to 375F.

Bring a pot of water to boil with some salt. Boil the ravioli for 3 - 5 minutes until they just start to float. If ravioli are thawed, less time will be needed.

Meanwhile, make the marinara. Drizzle olive oil in a skillet over medium heat with the onion, crushed red pepper, and a sprinkle of salt. Stir for 3 minutes until onions start to soften. Add the garlic and stir for 1 minute more. Add the tomatoes and sugar. Stir to combine and taste: add more salt to your preference.

Add the ravioli to the marinara and stir to coat.

For the dish, use a baking dish suitable for the amount of ravioli you are making. A 7-inch round casserole or equivalent is perfect for two! To assemble, layer half the ravioli and half the mozzarella, then repeat. Top with the parmesan. Reserve any extra marinara for serving or for another use.

Bake the ravioli at 375F for 20 - 30 minutes uncovered until the cheese is melted and slightly browned and ravioli is hot all the way through. Serve topped with fresh herbs if desired.