In a large skillet over medium heat, add olive oil and heat until shimmering.
Add the sliced onions and bell peppers to the skillet, sautéing until softened, about 5-7 minutes. Remove them from the skillet and set aside.
In the same skillet, increase the heat to medium-high and add the thinly sliced beef. Season with garlic powder, salt, and pepper. Cook until the beef is browned and cooked through, about 4-5 minutes.
Return the sautéed onions and peppers to the skillet with the beef mix, stirring to combine and heat through.
Preheat your oven to 350°F (175°C).
Slice the slider buns in half horizontally and place the bottom halves in a greased baking dish.
Spread mayonnaise evenly over the bottom halves of the slider buns.
Layer half of the provolone cheese slices on the buns, followed by the beef, onion, and pepper mixture. Top with the remaining provolone cheese slices.
Place the top halves of the slider buns over the cheese.
Cover the baking dish with foil and bake in the preheated oven for 15 minutes.
Remove the foil and bake for an additional 5-10 minutes or until the cheese is bubbly and slightly golden.
Slice the sliders and serve warm.
Notes
For an added kick, top with sliced jalapeños before serving.