1. Preheat oven to 375°.
2. Pierce bottom and sides of pastry shell with a fork. Bake at 375° for 15 minutes. Let cool on a wire rack. Increase oven temperature to 450°.
3. Heat a large nonstick skillet over medium-high heat. Add oil; swirl to coat. Add onion; sauté 8 minutes or until tender, stirring occasionally. Remove from pan; let cool.
4. Sprinkle onion, bacon, and cheese into pastry shell. Combine eggs and egg whites in a bowl, beating with a whisk. Add milk and remaining ingredients, beating with a whisk.
5. Pour milk mixture over cheese mixture in pastry shell. Place quiche on a baking sheet. Bake at 450° for 10 minutes. Reduce oven temperature to 350°. Bake at 350° for 40 minutes, shielding edges after 15 minutes, if necessary, to prevent excess browning. Let cool on wire rack 15 minutes. Cut into wedges, and serve immediately.