Place the four chicken breasts in the bottom of the slow cooker in a mostly even layer. There is no need to brown the chicken first, which keeps this recipe especially quick and makes cleanup simple.

Pour the entire jar of mild or medium salsa over the chicken, spreading it gently so the breasts are covered. The salsa supplies moisture, seasoning, tomato flavor, and the main source of heat for the dish.

Add the drained and rinsed black beans over the salsa-covered chicken. Rinsing removes excess canning liquid, helping the final mixture stay pleasantly thick instead of watery or overly salty.

Cover the slow cooker and cook on Low for 6-8 hours or on High for 3-4 hours. Begin checking based on the size of the chicken breasts, and continue until the meat is tender and reaches an internal temperature of at least 165°F (74°C).

Shred the cooked chicken directly in the slow cooker with two forks. Stir the shredded meat into the salsa and beans so every bite is coated, then let it sit in the warm sauce briefly before serving.

Spoon the fiesta chicken into tortillas, over rice, or into bowls. Add optional garnishes such as shredded cheese, avocado, sour cream, cilantro, or lime, keeping in mind that these extras are not part of the basic three-ingredient recipe.