Preheat oven to 400F degrees. Line a baking sheet with aluminum foil or parchment paper.
Open and drain the cans of tuna. Squeeze as much water out of the cans as possible.
In a mixing bowl, flake the tuna with a fork. Stir in the mayonnaise and relish until combined.
Place the slices of bread onto the prepared baking sheet. Divide the tuna mixture among the slices of bread. Top tuna filling with sliced tomato and provolone cheese.
Place into the oven until the cheese melts and starts to brown, about 10 minutes.