Heat the olive oil in a large pot over medium heat.
Add the sliced onions and a pinch of salt; sauté until caramelized, about 20 minutes.
Increase heat to medium-high; add chicken thighs, cooking until browned on both sides.
Pour in the chicken broth and add rice, bringing the mixture to a boil.
Reduce heat to low, cover, and simmer for 20 minutes or until rice is fully cooked.
Stir in thyme, salt, and pepper to taste, allowing flavors to meld for a few minutes.
Serve the rice in bowls, topped with generous amounts of grated Gruyère cheese.
Garnish with additional thyme if desired before enjoying your meal.