Place chicken thighs in a resealable plastic bag. Add red onion, lemon zest, ground cumin, lemon juice, and olive oil.
Seal and marinate in refrigerator for 3 hours. Occasionally turn bag to spread marinade evenly.
Set grill to 375°F (medium to high setting). Remove chicken from marinade; reserve excess marinade for basting.
Sprinkle chicken with salt and pepper. In a small saucepan, bring marinade to a boil.
Grill chicken for 12 minutes per side or until internal temperature reaches 165°F, basting occasionally with marinade. Remove from grill and serve with salsa.
For the salsa, in a medium bowl, mix the corn, tomato, red onion, cilantro, olive oil, lemon juice, cumin, and jalapeno. Peel, pit and dice avocado. Add to salsa and season with 1/4 tsp salt and 1/4 tsp pepper.