Butter one side of each slice of bread and place in the pan. Spread mayo on the insides of each slice of bread.
Put a slice of cheese on each bread slice. On one slice of bread, place the spring mix and turkey; and on the other slice, place the tomatoes seasoned with salt and pepper.
Place the bread, butter side down in the pan. Cover with a lid and cook until the bread is golden brown and the cheese has melted.