Start by trimming any excess fat from the chicken breasts. Cut each breast in half lengthwise to create thinner pieces that will cook evenly. Season the chicken generously with salt and fresh ground black pepper.
In your slow cooker, pour in the salsa. Lay the seasoned chicken pieces on top of the salsa, ensuring they are well coated. Drizzle the fresh-squeezed lime juice over the chicken.
Cover the slow cooker with its lid and cook on low for 6 to 8 hours, or on high for 3 to 4 hours. The chicken should be tender and easily shred with a fork when done.
About 15 minutes before serving, sprinkle the grated Mozzarella over the chicken. Cover again to allow the cheese to melt perfectly.
Once the cheese has melted, serve your Slow Cooker Salsa Chicken over rice, in tacos, or on a bed of greens for a fresh salad.