Melt 1 tablespoon of butter in a large skillet over medium heat. Sauté the onions and peppers until they start to caramelize, about 15 minutes. Add a few splashes of water periodically to aid in caramelization.
While they cook, add all the cheese whiz ingredients into a saucepan over medium-low heat. Stir frequently until the cheese melts, once it comes to a low simmering boil turn off the heat. The mixture will continue to thicken as it cooks.
Season the peppers and onions with a pinch of salt and transfer to a bowl.
In the same large skillet still over medium heat, add 1 tablespoon of butter. Add the steak in a single layer, and cook about 3-4 minutes undisturbed. Season with 1/2 tsp salt and 1 tsp pepper then flip the steak, using a spatula to break it up into bits as it cooks.
Once cooked through, turn off the heat and add the onion-peppers back into the pan and stir the combine with the steak.
Add ½ cup of cheese sauce into the steak mixture (or more/less based on your preference) and toss to evenly coat.
Turn the oven to broil, divide the sliders in half and place them face up on a pan to toast to golden brown. Watch closely to prevent browning.
Divide the steak mixture evenly over the bottom buns. To the top buns add provolone cheese slices. Place the pan back under the broiler until cheese melts and bubbles, about 2 minutes.
Place the top buns over the steak. Combine garlic and parsley with melted butter and brush it over the tops of the sliders. Serve with extra cheese whiz for dipping.