Preheat the oven

• Preheat the oven to 180 °C.

Cook the vegetables

• Heat the olive oil in a frying pan over medium heat.
• Sauté the onion and mushrooms until softened and lightly browned.
• Add the garlic and cook until fragrant.
• Add the spinach and cook until wilted, then season with salt and pepper.

Whisk the egg mixture

• Beat the eggs in a mixing bowl with the milk, salt and pepper.

Assemble the quiche

• Spread the cooked vegetables in the pie dish.
• Scatter the crumbled feta over the vegetables.
• Pour the egg mixture over the top and sprinkle with mozzarella.

Bake

• Bake until the center is set and the top is golden.

Rest and serve

• Let the quiche rest before slicing and serving.