Whisk together the mayo, relish, and ketchup in a bowl, Season with salt and pepper to taste. Spread on each slice of bread.
To build the sandwich, lay down one slice of bread and top with lettuce and tomato seasoned with salt and pepper, another slice of bread topped with cheese and turkey, then finally a top slice of bread. Place the toothpicks in to hold the sandwich together.
Cut diagonally from corner to corner to create 4 triangle pieces. (Serve 2 pieces per portion with pickles).