In a skillet over medium-high heat, cook bacon until done but not crispy. Set aside and cut into small pieces once cooled.
In the same skillet, sauté mushrooms in the remaining bacon grease until tender. Set aside.
Lightly oil or spray the pan and wilt the spinach until soft. Set aside.
In a large bowl, sift together flour, salt, baking powder, onion powder, and paprika.
In another bowl, beat together milk, melted butter, and eggs.
Slowly add wet ingredients to dry, stirring until well combined — the batter will be thin.
Fold in bacon, mushrooms, spinach, artichokes, feta, and gruyère.
Pour filling into the prepared crust. Bake at 350°F for 45–55 minutes, or until set in the center. If the crust browns too quickly, cover edges with foil or a pie crust shield.