Preheat your oven to 375°F (190°C) and grease a 12-cup muffin pan with cooking spray.

In a skillet over medium-high heat, add the sliced mushrooms and cook for about 2-3 minutes until lightly browned. Add the chopped spinach and cook for another minute until wilted. Remove from heat and let cool.

In a large mixing bowl, crack the 4 large eggs and whisk thoroughly. Add the grated Parmesan cheese, milk, garlic powder, onion powder, salt, and black pepper. Mix until smooth.

Fold in the cooled vegetable mixture gently into the egg mixture to evenly distribute.

Fill each muffin cup about three-quarters full with the mixture.

Bake for 18-20 minutes or until centers are set and a toothpick inserted comes out clean.

Allow muffins to cool in the pan for about 5 minutes before transferring to a wire rack.