1. 1. In a mixing bowl, combine drained tuna, mayonnaise, dijon mustard, and pickle relish. Mix well until all ingredients are evenly incorporated.

2. 2. Spread butter on two slices of bread.

3. 3. Spoon the tuna salad mixture onto one slice of bread.

4. 4. Top with the other slice of bread to form a sandwich.

5. 5. Cut the sandwich in half diagonally for serving.