Heat oven to 425°F. In medium bowl, place Bisquick mix. Cut in shortening, using pastry blender (or pulling 2 table knives through ingredients in opposite directions), until particles are size of small peas. Sprinkle with cold water, 1 tablespoon at a time, tossing with fork until all flour is moistened and pastry almost leaves side of bowl (1 to 2 teaspoons more water can be added if necessary).
Press pastry in bottom and up side of ungreased 9-inch quiche dish or glass pie plate. Bake 12 to 14 minutes or until crust just begins to brown and is set. Reduce oven temperature to 325°F.
Meanwhile, in 10-inch skillet, melt butter over medium heat. Cook onion and mushrooms in butter about 5 minutes, stirring occasionally, until tender. In medium bowl, beat eggs, milk and red pepper until well blended. Stir in spinach, bell pepper, mushroom mixture and cheese. Pour into partially baked crust.
Bake 40 to 45 minutes or until knife inserted in center comes out clean. Let stand 10 minutes before cutting.
