Preheat your oven to 350°F (175°C) and prepare a baking dish by greasing it.

In a medium mixing bowl, combine well-drained canned tuna, mayonnaise, Dijon mustard, celery, red onion, pickle relish, lemon juice, garlic powder, salt, and black pepper. Stir until creamy.

Slice the slider rolls in half horizontally and place the bottom halves in the baking dish.

Spread the tuna filling evenly over the bottom halves of the slider rolls.

Layer slices of cheddar cheese over the tuna mixture.

Place the top halves of the slider rolls back over the cheese and press down slightly.

Melt some butter and mix in parsley, garlic powder, and Dijon mustard. Brush this mixture over the top of the slider rolls.

Cover the baking dish with aluminum foil and bake for about 15 minutes. Remove the foil and bake for an additional 5-8 minutes until golden brown.

Allow to rest for a few minutes before slicing and serving warm.