To make the dressing, add the cilantro, jalapeño, green onions, lime juice, garlic, greek yogurt, mayo and ½ teaspoon salt to a blender. Blend until completely smooth. Transfer 2 tablespoons into a mixing bowl. Cover the remaining dressing with plastic wrap and set aside in the fridge until ready to use.
Pound the chicken breasts slightly to make them an even thickness throughout, this helps prevent them from drying out on the grill. Season with salt. Add the chicken breasts to the mixing bowl with the reserved dressing. Toss well to combine. Cover and let marinate in the fridge for at least 30 minutes but up to 8 hours.
Preheat an outdoor grill or indoor grill pan to medium high heat and lightly oil the grates. Place the chicken breast on the grill in an even layer. Cook for 4-6 minutes per side, until the chicken is nicely charred on both sides and cooked through. The internal temperature should be 165° F. Remove the chicken from the grill and rest 5 minutes. When the chicken is cool enough to handle, slice it on the bias.
To assemble the salad, add the romaine to a salad bowl. Top with the cherry tomatoes, red onion, cucumbers, mango, and black beans. Top with the sliced chicken. Drizzle the dressing on top of the salad and top with cilantro leaves.
Notes
** dressing makes 1 cup
** total salad makes about 9 cups