Heat olive oil in a skillet over medium-high heat; saute garlic until fragrant, about 1 minute. Add chicken; cook and stir until chicken is no longer pink in the center, 5 to 7 minutes.
Mix onion, red bell pepper, black beans, and cilantro into chicken; saute until onion is tender, about 5 minutes. Stir salsa into chicken mixture until heated through, 1 to 2 minutes.
Spoon chicken mixture into tortillas and top with Mexican cheese blend.