Preheat broiler to high with rack about 6 inches from heat.

Heat 2 tablespoons oil in a large oven-safe skillet (12 inches, broiler-safe) over medium.

Sauté 1 diced bell pepper, 1 cup sliced mushrooms, and ½ diced onion 5-6 minutes until softened.

Add 2 minced garlic cloves and 3 cups fresh spinach; cook 2 minutes until spinach wilts.

Whisk 10 eggs, ¼ cup milk, ½ cup grated Parmesan, 1 teaspoon salt, and ½ teaspoon black pepper in a large bowl.

Pour eggs over vegetables; stir gently to distribute evenly.

Cook on stovetop without stirring 5-7 minutes until edges set but center remains slightly jiggly.

Transfer the skillet to the oven and broil for 3-5 minutes until the top is puffed and golden brown. Check the center reaches 160°F; if it needs longer after browning, lower oven to 350°F and bake gently until done.

Remove from oven; cool 5 minutes.

Slice into wedges and serve warm or at room temperature.