Preheat oven to 350 degrees F. In a large skillet over medium heat, heat olive oil. Sauté onions until soft. Add the ground beef and stir to break up meat. Sauté until cooked through; drain fat.
Stir in fire roasted tomatoes and McCormick Original Chili Seasoning Mix, and season with salt and pepper. Simmer until liquid is slightly reduced. Remove from heat.
Coat a 9” x 13” baking dish with cooking spray. Place the bottom halves of the slider buns in the dish. Top with chili mixture. Sprinkle cheese over each slider. Place the top halves of the buns on top.
Brush the tops of the buns with the melted butter. Sprinkle garlic powder and salt on top.
Bake at 350 degrees F until the cheese melts and everything is warmed through, 15-20 minutes.