Meatless Baked Ziti

Name: Meatless Baked Ziti
Ingredients: 1 (16 ounce) package ziti pasta; 1 pound shredded part-skim mozzarella cheese; 1 (15 ounce) container whole-milk ricotta cheese; 1 cup grated Parmesan cheese, divided; 0.5 cup grated Romano cheese; 0.5 medium yellow onion, chopped; 0.25 cup chopped fresh parsley; 1 large egg; 2 teaspoons minced garlic; 1 teaspoon dried basil; 1 teaspoon dried oregano; 0.25 teaspoon ground thyme; salt and freshly ground black pepper to taste; 4 cups marinara sauce, divided