Grilling a sandwich can leave the inside contents only somewhat warm, especially if you prefer a shorter cooking time with slightly browned bread. However, steaming a sandwich prior to grilling it can result in a hot and moist interior. There may be occasions when steaming should be avoided, such as when you want to maintain the integrity of the ingredients inside. For example, if you want fried chicken strips to stay crunchy or lettuce to remain crisp, steaming the whole sandwich is not the way to go.
Assemble your sandwich with the desired ingredients.
Moisten a paper towel, and wrap it around the sandwich. The moisture in the paper towel will steam the sandwich.
Place the sandwich inside the microwave. Heat it on high for about 30 to 35 seconds.
Remove the sandwich from the microwave. Brush the exterior of the sandwich with melted butter, and place it on a hot grill pan.
Cook the sandwich to the desired texture, remembering to flip the sandwich over for even browning.