Preheat your oven to 350 degrees F and spray a 9 x13 casserole dish lightly with nonstick spray.
In a large bowl, combine the tuna, celery, red onion, relish, mayo, lemon juice, tomato, salt, and pepper. Set it aside.
Place bottom half of sliders into casserole dish cut side up. Brush with some melted butter and bake for 5 minutes.
Carefully layer your ingredients over the bottom buns, starting with 6 slices of Colby Jack cheese, then the tuna mixture, the remaining 6 slices of Colby Jack cheese, and the bun tops.
In a small bowl melt butter. Once melted brush it all over bun tops and then sprinkle garlic powder.
Bake in your preheated oven, uncovered, for 15-20 minutes or until the tops are toasted, cheese is melted and the sliders are heated throughout.
Allow to cool for a few minutes. Sprinkle with chopped chives right before serving. Slice and enjoy.