Preheat your oven to 180°C (160°C for fan-forced) and prepare a 20 x 30 cm baking dish by greasing it with olive oil or lining it with parchment paper.

In a large skillet, heat olive oil over medium-high heat. Sauté chopped brown onions for 3-4 minutes until soft and translucent.

Add minced garlic and sliced mushrooms, cooking for another 3-4 minutes until mushrooms turn golden brown.

Stir in fresh baby spinach and cook until wilted, about 1-2 minutes. Remove from heat and let cool slightly.

In a bowl, whisk together eggs and milk until combined. Add half of the Parmesan cheese, salt, and pepper.

Spread the cooled vegetable mixture evenly in the baking dish, then pour the egg mixture over the top. Sprinkle halved cherry tomatoes and remaining Parmesan on top.

Bake for approximately 30 minutes or until the top is golden and the center feels set when gently shaken.

Allow to cool for about 10 minutes before slicing. Serve warm with a green salad and sliced avocado.