Set oven to 400F.
Drain excess water from the package of tuna.
Combine all ingredients – except for the mushroom caps – into a large bowl. Mix together.
Remove stems from the mushrooms and scrape out the inside of the cap using a spoon.
Build the sliders. Evenly divide the tuna salad among the 3 sliders.
Top the tuna salad with a piece of mozzarella cheese and then add the mushroom cap as the top bun.
Skewer the entire slider with a wooden kabob stick.
Place the slider on a baking sheet and then wrap foil around the slider to keep it from moving in the oven.
Bake for 15 minutes at 400F.