Preheat your oven to 350°F (175°C).

Cook the sausage in a large skillet over medium heat until browned, about 5–7 minutes.

Add the diced mushrooms and spinach, stirring until the spinach wilts down, about 2–3 minutes.

Whisk together the eggs, milk, salt, and pepper in a bowl until frothy.

Layer the cooked sausage mixture in a greased baking dish. Pour the egg mixture evenly over it and top with shredded cheese.

Bake in the preheated oven for 30–35 minutes, or until the eggs are set and the top is golden brown.

Let it cool slightly before slicing.