1. Mix all the ingredients except the chicken in a large bowl.
2. Add the chicken to the mixture and coat evenly.
3. Cover the bowl and refrigerate for at least 4 hours or overnight.
4. Preheat the grill.
5. Remove the chicken from the marinade and discard the marinade. (This protects against cross-contamination.) Sprinkle the chicken with the salt and pepper.
6. Place the chicken on the hot grill and cook until the juices run clear, 6 to 8 minutes per side.
For the corn salsa:
1. Heat the oil in a skillet over medium heat. Add the corn and cook for 2 minutes. Add the sugar, season with salt and pepper and cook for another minute. Add the vinegar and cook for 1 more minute.
2. Transfer the corn into a small bowl and cool slightly. Stir in the tomatoes, onion, cilantro and jalapeño pepper. Adjust the salt and pepper to suit your taste. (This can be made in advance and stored in the refrigerator for up to 2 days.)
3. Spoon the salsa over each piece of grilled chicken.