In a small bowl, whisk together 1/4 cup cilantro, 1/4 cup lime juice, 2 tablespoons olive oil, minced garlic, cumin, salt, and pepper.
Place chicken breasts in a shallow dish or resealable bag, pour the marinade over the meat, and refrigerate for 30 to 60 minutes.
Preheat an outdoor grill or indoor grill pan to medium-high heat. Lightly oil the grates.
Grill the chicken for 6 to 8 minutes per side, or until the internal temperature reaches 165°F (74°C). Remove from heat and let rest for 5 minutes.
While chicken rests, prepare the salsa by gently tossing the diced mango, avocado, red onion, jalapeño, remaining cilantro, and remaining lime juice in a bowl.
In large serving bowls, create a base with chopped Romaine lettuce, black beans, and corn.
Slice the rested chicken into strips and place atop the salad base.
Garnish each serving with a generous portion of the mango avocado salsa and drizzle with remaining pan juices or extra lime if desired.