In a large pot, heat olive oil over medium heat. Add chopped bell peppers, sliced red onion, and minced garlic. Sauté for 3-5 minutes until softened.

Add the chicken breasts, black beans, diced tomatoes, chicken broth, and fajita seasoning to the pot. If using brown rice, include water now. Stir to combine.

Bring to a boil, then reduce heat and let it simmer for 20 minutes, covered.

Remove chicken, shred it, and return it to the pot, stirring it in.

Simmer uncovered for another 10-15 minutes until the rice is tender and the broth thickens. Adjust seasoning if needed.