Thaw fish, if frozen.
For stuffing, in a mixing bowl stir together egg white, croutons, cottage cheese, carrot, and cocktail sauce.
Stir in the drained spinach.
Spray four 10 ounce custard cups with nonstick spray coating.
Line cups with fish fillets, trimming and piecing as necessary.
Spoon stuffing into the center of each cup.
Arrange filled cups in the microwave.
Cover loosely with waxed paper.
Cook on high for 5 to 6 minutes or till fish flakes easily when tested with a fork and stuffing is heated through.
Rotate and rearrange the cups once during cooking.