In a hot skillet, melt 1 tablespoon of butter, then add the onion, mushrooms, and bell pepper. Sauté until they're golden and softened. Set them aside.
In the same skillet, increase the heat and sear the sliced beef until browned. Season with salt and black pepper, then remove from heat.
On a baking sheet, arrange the bottom halves of the slider buns. Layer the beef, sautéed vegetables, and provolone cheese on top. Cover with the top halves of the buns.
Melt the remaining 2 tablespoons of butter and mix in the minced garlic. Brush this mixture over the tops of the buns.
Bake at 350°F for about 15 minutes, or until the sliders are golden and the cheese is fully melted.
Serve these Philly cheesesteak sliders warm and enjoy the delicious flavors!