Preheat the oven to 400°F.
In a small bowl, stir together the mayonnaise,ketchup, and Worchestershire sauce and set aside.
Heat a large oven-safe skillet over medium-high heat. Melt the butter, then add onion and pepper; cook for 7 to 8 minutes, stirring often, until the onion is translucent and beginning to carmelize. Remove from the pan and set aside.
Add the beef to the pan, and season with salt, pepper, and garlic powder. Cook for about 10 minutes or until browned, breaking it apart as it cooks. Add the frozen cauliflower rice and cook for another 2 to 3 minutes, until there is no liquid left in the pan and the cauliflower rice is tender. Stir the pepper and onion into the beef mixture.
Remove the skillet from the heat and stir in two-thirds of the mayonnaise mixutre. Top with the shredded cheese. Put the skillet into the oven and bake for 5 to 7 minutes or until the cheese melts. Carefully remove the skillet from the oven and drizzle with the remaining sauce.