Preheat oven to 300F and line a sheet pan with parchment paper.
Heat 2 Tbsp neutral oil in a large skillet over medium-high heat and add 1 large sliced green bell pepper, 1 large sliced red bell pepper, and 1 large sliced brown onion.
Season with salt and pepper and sauté 8-10 minutes until softened and caramelized.
Transfer vegetables to a bowl and set aside.
Add 2 Tbsp butter to the same skillet and melt, then add 1 3/4 lbs shaved steak.
Break steak into bite-sized pieces and cook 4-5 minutes until no longer pink.
Stir in 2 tsp garlic powder, 2 tsp Worcestershire sauce, salt, and pepper.
Reduce heat to medium-low and add the cooked peppers and onions back to the pan along with half of 1 lb provolone cheese.
Stir until cheese melts and everything is combined, then set aside.
Cut 2 packages Hawaiian rolls in half horizontally, keeping each half intact.
Spread 1/4 cup mayonnaise on each of the 4 cut surfaces.
Spread steak filling evenly over both bottom halves and top with remaining cheese.
Place top halves over the filling.
Melt remaining 1 Tbsp butter and mix with 1 tsp minced parsley and a pinch of salt.
Brush parsley butter over the tops of both sets of rolls.
Bake 12-15 minutes until filling is warmed through and tops are golden-brown.
Slice into individual sliders along the roll perforations and serve immediately.