Preheat and Prep : Preheat your oven to 375°F (190°C). Lightly grease a baking dish with olive oil or non-stick spray.

Cook the Spinach : Heat olive oil in a large skillet over medium heat. Add the garlic and onion, cooking until fragrant and translucent, about 3–4 minutes. Gradually add the spinach to the skillet, cooking until wilted. Remove from heat and let cool slightly.

Prepare the Cheese Mixture : In a large bowl, combine the ricotta, Parmesan, and mozzarella cheeses. Add the Italian seasoning, red pepper flakes (if using), salt, and pepper. Mix well. Stir in the beaten eggs to bind the mixture.

Combine and Assemble : Fold the cooked spinach mixture into the cheese mixture until evenly combined. Transfer the mixture to the prepared baking dish, spreading it out evenly.

Add the Topping (Optional) : If using the topping, mix the breadcrumbs with melted butter and sprinkle evenly over the spinach mixture.

Bake : Bake in the preheated oven for 25–30 minutes, or until the top is golden and bubbly. Remove from the oven and let the bake cool for 5 minutes before serving.