Cheesy Spinach & Mushroom Casserole

Preheat oven to 350°F. Coat an 8-inch-square baking dish with cooking spray. Heat oil in a large skillet over medium heat. Add onion and cook, stirring, until softened and starting to brown, about 4 minutes.Add mushrooms and garlic; cook, stirring, until the mushrooms have softened, about 4 minutes. Transfer to a large bowl.

Add spinach, 1 cup cheese, eggs, milk, salt and pepper to the mushroom mixture. Stir until well combined. Transfer to the prepared baking dish, cover with foil and bake for 40 minutes. Remove from the oven and sprinkle with the remaining 1/2 cup cheese. Bake, uncovered, until the cheese is melted, about 5 minutes more.