Preheat your oven to 350°F (175°C).
In a large skillet over medium heat, add the chopped spinach and sauté for 2-3 minutes until it wilts. Remove from heat and let it cool slightly.
In a mixing bowl, combine the ricotta cheese, mozzarella cheese, and Parmesan cheese. Stir until well combined.
In another bowl, whisk the eggs, milk, garlic powder, onion powder, black pepper, and salt together. Add this mixture to the cheese mixture and stir well.
Fold in the sautéed spinach until evenly distributed.
Grease a 9x13 inch baking dish with olive oil. Pour the spinach and cheese mixture into the dish.
In a small bowl, combine the breadcrumbs with the red pepper flakes (if using). Sprinkle the breadcrumb mixture evenly over the casserole.
Bake in the preheated oven for 30 minutes or until the casserole is set and the top is golden brown.
Remove from the oven and let it cool slightly before serving.