Prepare a grill fire to 350°.
Pat steak dry with paper towels and coat both sides with olive oil and steak rub.
Grill the steak over indirect heat with the grill closed about 5 minutes, flip the steaks and continue to grill until internal temperature reaches 130° using a digital meat thermometer.
Meanwhile, slice the onions and peppers. Place on a grill pan and toss with olive oil, salt and pepper.
Remove the steaks from the grill and allow to rest 15 minutes before slicing.
Add the onions and peppers to the grill.
Cook for 10 - 15 minutes with the grill closed, stirring the vegetables every 5 minutes, until vegetables are softened.
Remove from grill.
Preheat oven to 400°.
Slice the steak into thin slices.
Prepare the cheese sauce by adding Velveeta, milk, smoked paprika, garlic and black pepper to a saucepan.
Cook over medium heat, whisking until cheese is melted and smooth. Remove from heat.
Add bottoms of slider buns to a baking pan.
Layer steak over the buns.
Top with onions and peppers.
Drizzle cheese sauce over the top.
Add the top of the buns.
Brush with melted butter.
Cover with foil and bake for 15 minutes.
Remove from oven and use a sharp knife to slice the buns into individual sandwiches.
Serve immediately.