Preheat oven to 400 degrees F. Line a baking sheet with a silicone mat or aluminum foil sprayed with cooking spray. Bake fish sticks 20 minutes, turning once, or until golden brown and crispy.
Meanwhile, stir together yogurt, mayonnaise, and relish. Spread yogurt mixture evenly over all slices of bread.
For each sandwich, arrange a single layer of chips on one slice of bread. Arrange lettuce over chips, fish sticks over lettuce, and then top with tomato slices. Place the other slice of bread on top, cut in half, and serve.