Grill peppers, corn and onion over medium high heat on a lightly greased rack for 10 minutes or until tender, turning. Remove the pepper and onion from heat and set aside. Grill the corn for another 10 minutes or until tender. Cool slightly, and cut the corn from the cob, placing into a bowl. Put the pepper into a resealable plastic bag and let stand 10 minutes to loosen skin. Remove the charred skin. Chop the onion and pepper, and add to the corn. In another small bowl, combine remanining ingredients. Add mixture to corn and toss to coat. Serve.