There are about 1,000 combinations out there for matching up turkey, cheese, and bread. This recipe uses dill Havarti for its meltability and hint of herb-y sweetness, but you can try this with pretty much any other cheese and not go wrong. Either way, you'll have a superior turkey sandwich in the time it takes to preheat your broiler.
Preheat the broiler.
Divide the turkey between 2 of the bread slices, and top evenly with the cheese. Transfer to a foil-lined baking sheet and broil until turkey is warmed and cheese is melted, 4 to 5 minutes. Meanwhile, spread the mustard on the remaining slices of bread.
Top the turkey and cheese with the tomato slices and the remaining bread. Serve with pickles.