In a large skillet or frying pan, add olive oil. Bring to a medium high heat, until the oil is shimmering.
Add onion, garlic, and bell pepper. Saute until onion is translucent and peppers are tender, about 5-6 minutes.
Move sauteed onion and peppers aside. Add the cut leftover prime rib beef slices and heat through, about two minutes. Combine meat and sauteed onion and peppers, then season with salt and pepper.
Divide the cooked meat into your 4 sandwich portions and top with provolone and white American cheese slices (total 2-3 slices per sandwich). Once the cheese has melted, transfer portions to toasted sandwich rolls using a spatula.