1. Preheat oven to 425 degrees. Heat oil in a large saucepan over medium heat. Add onion and garlice, and season with salt and pepper; cook, stirring occasionally, until softened, about 5 minutes. Add oregano and tomatoes. Bring to a boil, reduce heat, and simmer, breaking up tomatoes with spoon, until sauce is thickened and reduced to about 5 1/2 cups, 20 to 25 minutes.

2. Meanwhile, cook ravioli in a large pot of boiling salted water just until they float to the top (pasta will continue to cook in oven), Drain pasta, return to pot.

3. Toss sauce with pasta. Pour pasta into a large gratin dish or 9 by 13-inch baking dish, and sprinkle with cheeses. Bake until golden, 20 to 25 minutes. Cool slightly before serving.