RESERVE 2 Tbsp. chocolate chunks; set aside.
BEAT eggs in large bowl with fork. Add whipped topping, crumbs and remaining chocolate chunks; stir just until blended. Spread into greased 1-1/2- or 2-quart microwavable round dish at least 2 inches deep.
MICROWAVE on MEDIUM (50%) 5 minutes. Rotate dish half turn. Microwave on HIGH 4-1/2 to 5-1/2 minutes or until cake starts to pull away from side of dish and is just slightly moist.
PLACE serving plate on top of dish; invert cake at once. Remove pan. Sprinkle hot cake with marshmallows and reserved chocolate chunks.