In a medium frying pan, cook diced onion and garlic with a bit of vegetable oil (or cooking spray) over medium-high heat until translucent and tender. Add in fresh spinach and mushrooms, salt and pepper, and cook until just wilted. Set aside to cool for a few minutes. Add feta and cheddar.
In a large mixing bowl, whisk together eggs, flour, and baking powder. Add salt and pepper. Whisk in milk, then stir in spinach-onion mixture.
Pour quiche base into prepared pan. After 14 mins, add some more
Cheddar on top.
Bake for 18 minutes, or until center is set and the outside edge is golden brown.