In a large skillet, heat the olive oil over medium heat. Add the sliced onions and cook, stirring occasionally, until they are caramelized and golden brown, about 15-20 minutes. Add the minced garlic and sauté for an additional 2 minutes until fragrant. Remove from heat.
In the same skillet, add the ground beef. Cook over medium-high heat until browned, breaking it up with a spatula as it cooks. Drain any excess fat.
In a large mixing bowl, combine the cooked beef, caramelized onions and garlic, uncooked rice, beef broth, Worcestershire sauce, thyme, salt, and pepper. Mix well until all ingredients are evenly combined.
Pour the mixture into a greased 9x13 inch baking dish. Spread it out evenly.
Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, carefully remove the foil and sprinkle the shredded Swiss cheese evenly over the top. Return to the oven and bake uncovered for an additional 10-15 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it sit for 5 minutes before serving. Garnish with freshly chopped parsley.
Notes
Let the casserole sit for a few minutes before serving for better slicing.