Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish or a large ovenproof skillet.

Cut the refrigerated biscuit dough into quarters and distribute it evenly across the bottom of your prepared dish.

In a large mixing bowl, whisk together the eggs and whole milk until fully combined and fluffy. Add salt, black pepper, and smoked paprika.

Fold in the cheddar, mozzarella, and Parmesan cheeses, then add the bell pepper, onion, and spinach, stirring gently to combine.

Pour the egg mixture over the biscuit pieces, pressing down gently to ensure they soak up the mixture.

Drizzle melted butter over the top and bake for 25 to 30 minutes until puffed and golden brown.

Allow the frittata to cool for 5 minutes, then slice and serve warm.