Lightly grease a 10-inch quiche/tart pan (or a 9-inch pie plate)
Prepare Stuff. For instance, in a medium frying pan, cook onion and mushrooms with a bit of vegetable oil (or cooking spray) over medium-high heat until onions are translucent and tender, and mushrooms are browned. Set aside to cool for a few minutes. Add sausage-like bits.
In a large mixing bowl, whisk together eggs, flour, baking powder and salt. Whisk in milk, then stir in Stuff mixture.
Pour quiche base into prepared pan. Top with Parmesan cheese.
Bake for 25 minutes (30-35 minutes in a pie plate), or until center is set and the outside edge is golden brown.