Preheat oven to 350°F (175°C).

In a skillet, heat olive oil over medium heat. Add Italian sausage, onion, and bell peppers; cook until sausage is browned and vegetables are tender.

Stir in garlic and spinach; cook until spinach is wilted.

In a large bowl, whisk together eggs, milk, Italian seasoning, salt, and black pepper.

Add the sausage and vegetable mixture to the egg mixture. Mix well.

Grease the baking dish and pour the mixture into it. Drop spoonfuls of ricotta cheese on top and sprinkle with Parmesan cheese.

Cover with foil and refrigerate overnight.

In the morning, bake uncovered for 50-55 minutes or until the center is set and golden brown.