Preheat oven to 350°F.
Cut bell peppers and onions into thin strips.
Heat 1 Tbsp. oil in a pan. Add peppers and onions, along with a pinch of salt and pepper, and saute on medium for about 10 minutes. Allow the onions to caramelize, then remove peppers and onions and set aside.
Cut top sirloin steak into thin strips. Return the pan to the stove and add the beef strips. Season with a generous pinch of salt and pepper as well as 1 tsp. garlic powder. Saute for 2-3 minutes on each side on slightly above than medium heat. When the steak is almost cooked, but not quite done, remove it from the stovetop.
Halve your slider buns or Hawaiian rolls. Place the bottom half of the rolls in an 11x17" baking dish. Layer the buns with steak and juices, then peppers and onions, and finally a slice of provolone on each slider. Replace the tops of the buns.
Making the garlic herb butter: Add butter to a small microwaveable bowl. Melt in the microwave in 30-second increments until fully melted. Add remaining garlic powder, Italian seasoning, and red chili flakes to the butter and stir to combine.
Brush the garlic herb butter on top of the sliders. Bake for 15 minutes, allowing the cheese to melt and the tops of the buns to become golden. Serve, and enjoy!