Rub the corn with 2 tablespoons of the oil and season with salt and pepper. Put the corn directly on the grill grates (or put in a baking pan if using oven method) and cook until the kernels are slightly charred on all sides, turning every couple of minutes. Remove from the heat. Using a sharp knife, carefully cut the kernels off of the cobs and put in a mixing bowl. Add the avocado, lime juice, onions, bell peppers, jalapeno, cilantro, vinegar, and remaining 1 tablespoon of oil. Season with salt and pepper.
Divide the mixed greens evenly among 4 plates. Drizzle the reserved mango marinade over the greens. Top with shrimp and mango skewers and a couple of spoonfuls of the roasted corn and avocado salsa. Garnish with some chopped cilantro serve with remaining salsa on the side.
Thread the shrimp and mango onto separate skewers and put side-by-side in a baking dish. Pour the remaining marinade over the shrimp and mango; cover with plastic wrap. Put in the refrigerator and allow to marinate for about 30 minutes, flipping the skewers occasionally.