In a large skillet, heat the avocado oil over medium-high heat. Season the chicken with salt, pepper, and garlic powder on both sides. Add them to the skillet and cook for about 3-4 minutes per side until golden brown. They do not need to be fully cooked yet. Remove and set aside.

In the same skillet, add the sliced onions and butter. Cook for about 20-25 minutes, stirring occasionally, until caramelized and golden. Add the minced garlic and cook for another minute.

Stir in the balsamic vinegar and Worcestershire sauce. Sauté for a couple of minutes, then add the beef broth, heavy cream, and thyme and bring to a simmer.

Stir in the rice and return the chicken to the skillet. Cover and let it cook on low heat for about 20-25 minutes or until the rice is tender and has absorbed most of the liquid. Check partway through to make sure there's enough liquid; if it runs low, add ½ cup of water.

Once the rice is cooked, fluff the rice gently, then sprinkle the shredded cheese on top. Cover and let it cook for an additional 5 minutes until the cheese is melted and bubbly.

Serve everything straight from the skillet. Top with fresh chives and enjoy!