Preheat your oven to 350°F (175°C).

In a large skillet over medium heat, add the olive oil. Once hot, toss in the sliced onions and bell peppers and sauté until softened and beginning to caramelize, about 5-7 minutes.

Add the minced garlic and cook for an additional minute until fragrant.

Raise the heat slightly and add the sliced beef to the pan. Season with salt, pepper, and Worcestershire sauce if using. Cook until the beef is browned and cooked through, about 5-10 minutes. Remove from heat.

In a large mixing bowl, combine the sautéed beef and vegetables with the cauliflower rice. Mix well.

Transfer the mixture to a greased 9x13 inch baking dish and spread it out evenly. Top with shredded cheese.

Place the casserole in the preheated oven and bake for about 20-25 minutes, or until the cheese is bubbly and golden brown.

Let the casserole sit for a few minutes before serving. Garnish with fresh parsley.