Slice the turkey sausage link in thirds lenghtwise. Indoors or outdoors, grill the portabello mushrooms and sausage.
Chop the onion and asparagus. In about 1 tbls. of water, microwave the chopped asparagus for about 2 min. Then add 2 tbls. of milk and 2 slices of american cheese broken into pcs. Microwave about 1 min. Add diced onion, stir to make sure cheese is melted.
Place one portabello mushroom, cap down on plate, top with lettuce and sausage, drizzle with cheese sauce and place tomatoes on, the top with remaining portabello, cap up.