To make the salsa: Grill the bell peppers over Direct Medium heat until they are blackened and blistered all over, 12 to 15 minutes, turning occasionally. At the same time, lightly brush or spray the corn with oil and grill over Direct Medium heat until browned in spots, 10 to 12 minutes, turning occasionally. Place the peppers in a medium bowl and cover with plastic to trap the steam. Set aside for at least 10 minutes, then peel the skins from the peppers, discard the stems and seeds, and cut into 1/4-inch dice. When the corn is cool enough to handle, use a sharp knife to cut the kernels off the cobs. In a medium bowl, mix the peppers and corn with the remaining salsa ingredients.