Preheat your oven to 375°F and grease a 9x13-inch baking dish.

Heat 1 tablespoon of olive oil in a skillet over medium heat. Add sausage and cook until browned and fully cooked, about 6–8 minutes. Transfer to a plate.

In the same skillet, add the remaining tablespoon of olive oil. Add mushrooms and cook for 5 minutes until browned. Stir in spinach and sauté until wilted. Remove from heat.

In a large bowl, whisk together eggs, milk, salt, and pepper until smooth.

Add the cooked sausage, vegetables, and shredded cheese to the egg mixture. Stir well to combine.

Pour mixture into the prepared baking dish and smooth the top.

Bake for 30–35 minutes or until the center is just set and edges are golden.

Let cool for 5 minutes before slicing and serving.