Remove husks from corn. Place on pre-heated grill, 5 minutes on each side while basting with butter mixture. Grill for approximately 10 minutes total. Remove from heat and set aside. Using a melon baller or small ice cream scoop, scoop watermelon. Cut the strawberries into bite sized pieces. Chop purple onion and avocado.Chop herbs such as parsley or cilantro finely. Add all the ingredients to a bowl, including the corn from the cob, lime juice, and salt. Stir until combined and enjoy.