Cheesy Layered Baked Ziti

Ingredients

• 8 ounces shredded mozzarella cheese, divided
• 1/2 cup finely grated Parmesan cheese, divided
• 2 tablespoons olive oil
• Freshly ground black pepper
• 1 cup whole-milk ricotta cheese
• 5 cups marinara sauce
• 1 teaspoon kosher salt
• 1/2 teaspoon red pepper flakes
• 3 cloves garlic, finely chopped
• 1 pound dried ziti or penne pasta
• 1 medium yellow onion, finely chopped
• 1/4 teaspoon kosher salt