Heat the sausage in a skillet over medium heat just until warmed.
Assemble sandwiches. Spread half of the mustard on two slices of bread. Layer the sausages, lettuce, and tomatoes on top.
With the other half of the bread, top with the cheese.Place in the microwave for 15-20 seconds or until slightly melted. Place on top of the sandwich and slice in half and enjoy!