Preheat the oven to 350°F (180°C).
Wash the bell peppers, slice off the tops, and remove the seeds and membranes.
Peel the carrot and onion. Dice the onion and grate the carrot. Finely chop the garlic.
Cut the chicken thighs into small pieces.
Heat a skillet with a bit of olive oil over medium heat. Add the diced onion, grated carrot, garlic, mushrooms, and chicken to the skillet, cooking until the chicken is no longer pink and the vegetables soften.
Season the chicken mixture with paprika, cumin, salt, and black pepper. Stir to combine.
In a separate pot, boil the rice for 7-10 minutes until it’s slightly undercooked. Drain and set aside.
Combine the partially cooked rice with the chicken and vegetable mixture in a large bowl. Mix well and adjust the seasoning if needed.
Stuff each bell pepper with the chicken and rice mixture and place them upright in a baking dish. Add a little water or tomato juice to the bottom of the dish for moisture.
Cover the dish with foil and bake for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 10-15 minutes until the tops of the peppers are lightly browned.