Preheat oven to 400 degrees. In a large skillet over medium-high heat , melt butter. Saute onion until softened, about 5 minutes. Stir in flour, garlic powder, salt and black pepper; cook and stir for 1 minute. Stir in green chiles; remove skillet from heat and allow to cool slightly. Meanwhile, beat the eggs in a large mixing bowl; add the heavy cream and baking powder, and whisk vigorously. Stir in the cooled vegetables, and all remaining ingredients, mixing well. Set pie shell onto a foil-lined baking sheet, and then pour mixture into pie shell. Bake for 10 minutes at 400 degrees, then reduce oven temperature to 350 degrees and bake 30 minutes longer, or until set. Allow quiche to rest for 5 minutes prior to cutting into wedges for serving.