Preheat the grill over medium-high heat and preheat the oven to 275 degrees F.
For the slider:
Coat a saute pan with oil and put over medium-high heat. Add the peppers and onions and saute until tender.
For the beef on 'weck:
Rub the roast with olive oil and sprinkle with salt and pepper, to taste. Sear on the grill, then transfer the meat to a roasting pan. Put it into the preheated oven until it reaches desired temperature. Remove the roast from the oven to a cutting board and let it rest before slicing. Fill the rolls with the beef and arrange on plates with dollop of horseradish.
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