To prepare chicken, combine first 3 ingredients in a large zip-top plastic bag. Add chicken to bag; seal and marinate in refrigerator for 1 hour, turning bag occasionally.
To prepare salsa, combine watermelon and next 8 ingredients (through jalapeño); cover and chill until ready to serve.
Remove chicken from marinade; discard marinade. Sprinkle chicken evenly with 1/4 teaspoon salt. Place chicken on a grill rack coated with cooking spray. Grill 6 minutes on each side or until done. Remove chicken from grill; let stand 5 minutes. Cut chicken diagonally across grain into thin slices; serve with salsa. Garnish with cilantro sprigs and serve with lime wedges, if desired.