In a skillet, over medium-high heat, cook the bacon until the fat releases and it is cooked, but not crispy (about 10 minutes). Remove from skillet, retaining the grease, and set aside to cool. (Once it is cooled, use kitchen shears to cut into half-inch pieces.)
Add the sliced mushrooms to the skillet and sauté in the bacon grease until tender. Remove from skillet and set aside.
In the same pan, add a little oil or spray lightly with cooking spray and add the spinach leaves. Cook until tender and slightly wilted. Set aside.
In a large mixing bowl, sift together the flour, salt, baking powder, onion powder and paprika.
In a separate bowl, beat together the milk, butter and eggs.
Slowly add the egg mixture to the flour mixture and mix until well combined. The batter will be very thin.
Add the bacon pieces, mushrooms, artichoke hearts, feta, gruyere and spinach to the batter and mix with a wooden spoon to combine.
Pour the filling into the crust and bake at 350℉ for 45-55 minutes, or until the quiche is cooked through. If the crust starts browning too much, cover it with a pie crust shield or make your own with foil.