Place the thin sliced roast beef in the center of the foil and fold up all four sides to completely enclose the beef.
Bake in the preheated oven for 10 to 15 minutes.
While the beef is heating up, heat the cheese sauce ingredients in a small saucepan over low heat until the cheese has melted. Reduce heat to a simmer to keep warm.
Combine all the ingredients for the red ranch sauce in a small bowl. Mix well and set aside.
Melt the butter in a pan over low heat and place the onion roll open side down to toast each side of the bun.
Build the sandwich by spreading red ranch sauce on the bottom bun, and the layers of roast beef, and top with the warm cheese sauce.
“Success is no accident. It is hard work, perseverance, learning, studying, sacrifice, and, most of all, love of what you are doing or learning to do” – Pele, Brazilian soccer player