Preheat oven to 350°.
Melt butter in a nonstick skillet over medium heat. Add onion to pan; cook 15 minutes or until golden brown, stirring occasionally. Spread mixture in a single layer in an 11 x 7-inch baking dish coated with cooking spray. Combine egg substitute, 2 tablespoons cheese, salt, pepper, and eggs. Pour egg mixture evenly over onion; sprinkle with remaining 2 tablespoons cheese. Bake at 350° for 20 minutes or until set. Cool slightly; cut into 24 pieces. Top each with 1/2 teaspoon sour cream and 2 chive pieces.