Preheat the oven to 350°F (180°C).
Clean the mushrooms and carefully remove the stems to create space for the filling.
Lightly brush the mushrooms with olive oil, then place them on a baking sheet lined with parchment paper.
Sprinkle the finely chopped vegetables and spinach inside the mushroom caps.
Crack one egg into each mushroom cap.
Season with salt and pepper, then sprinkle with a little cheese if you like.
Bake for 15 to 20 minutes, until the egg white has set but the yolk remains creamy.