Combine salsa and beans in a bowl. Place one-third of tortilla strips in an 11 x 7-inch baking dish coated with cooking spray. Top with 1/3 cup cheese and about 1 cup salsa mixture. Repeat procedure with one-third of tortilla strips, 1/3 cup cheese, and remaining salsa mixture; top with remaining tortilla strips.
Combine sour cream and next 4 ingredients (sour cream through egg whites); stir with a whisk. Stir in onions. Pour over tortilla strips; sprinkle with 1/3 cup cheese. Cover and chill 8 hours or overnight.
Preheat oven to 350°.
Remove dish from refrigerator. Let stand at room temperature 10 minutes. Cover and bake at 350° for 20 minutes. Uncover and bake an additional 15 minutes or until lightly browned.