8 slices whole wheat bread
1 (12 ounce) can fully cooked luncheon meat (such as SPAM®), cut into 1/4 inch slices
8 slices Cheddar cheese
2 large tomatoes, cut into 1/2-inch slices
1 sweet onion, thinly sliced
¼ cup softened butter
Spread the mustard onto one side of each of the bread slices. Place the luncheon meat onto half of the bread slices, then top each with 2 slices of Cheddar cheese, sliced tomato, and onion. Place the remaining bread slices, mustard-side-down onto the onions. Spread butter evenly onto the outside of each sandwich. Heat a large skillet over medium-low heat. Place the sandwiches into the skillet, and cook until they are golden brown, then flip the sandwiches over, and continue cooking until golden brown and crispy on the other side, about 6 minutes per side. Allow the sandwiches to cool slightly before serving.