Preheat oven to 250°F. Spread 4 slices of bread with 1 tsp. mustard each. Top each with one-fourth of turkey, 1/4 cup cheese and 2 slices of pickle.
Place second slice of bread on top and press with palm of your hand to compress sandwich.
Melt half of butter in a large skillet over medium-high heat. Working with 2 sandwiches at a time, "grill" sandwiches until lightly browned, about 3 minutes per side. Keep warm in preheated oven. Wipe out skillet with paper towels, add remaining 1/2 Tbsp. butter to skillet, and prepare 2 remaining sandwiches. Serve with coleslaw, carrot-raisin salad and baked potato chips, if desired.