In a large skillet over medium-high heat, heat oil. Sprinkle chicken with taco seasoning and cayenne; season with salt. Add chicken and cook, turning halfway through, until golden brown and an instant-read thermometer inserted into thickest part registers 165°, 8 to 10 minutes per side. Transfer to a plate.
Add bell peppers, onion, and garlic to skillet and cook, stirring, until softened, about 7 minutes. Stir in beans until warmed through, then transfer mixture to another plate.
Reduce heat to low and return chicken to skillet. Top with cheddar and bean mixture, then cover and let cheese melt.
Top with cilantro and serve with tortilla chips, if desired.