Combine the soy sauce and maple syrup in a bowl. Add the sirloin cubes and stir to coat. Cover and marinate 1 hour. Remove the sirloin cubes, reserve the marinade. Alternately place the sirloin cubes, pineapple chunks and green pepper squares on a wooden or plastic skewer. Place the kabobs in an 8" square microwave or glass baking dish. Brush with the marinade. Cover with wax paper. With the microwave on HIGH, cook for 4 minutes. Rotate the dish a quarter turn and brush with the marinade. Re-cover with wax paper. Continue cooking in the microwave on MEDIUM for 4 minutes. Allow to rest 4 minutes before serving. Brush with the remaining marinade just before serving. NOTE: Adjust the microwave times if you change the size of the recipe. Yield: 8 servings, each 80 calories 1 medium fat exchange, carbohydrates:1