Slice the red bell pepper, green bell pepper, and onion into slivers.
Heat 1 tablespoon of oil in a large sauté pan over medium-high heat. Add the sliced peppers and onion (and jalapeño, if using). Sauté for 5-7 minutes until tender. For char marks, cook a bit longer. Remove veggies to a bowl and set aside.
Add another tablespoon of oil to the pan. Add the sliced chicken breast and season with kosher salt and black pepper. Cook, stirring, until no longer pink (about 4-5 minutes).
Add drained black beans to the pan with the chicken. Sprinkle cumin and chili powder over the mixture. Stir to combine and cook for 2-3 minutes, until it begins to bubble.
Return the cooked peppers and onions to the pan. Stir and cook everything together for 3-4 minutes, until heated through.
Serve immediately in flour tortillas or over rice, salad, or in a bowl. Top with cheese, sour cream, cilantro, salsa, and guacamole as desired.