1. Peel the husks of the corn down to the bottom of each ear without detaching and remove silk. Replace husks and secure with twine. Soak corn in a large bowl of cold water at least 30 minutes before grilling.
2. Prepare grill. Drain corn and grill corn and chiles, about 10 minutes for chiles and 15 minutes for corn, turning every 5 minutes, or until tender and evenly charred. Cover vegetables and let stand 10 minutes.
3. When cool enough to handle, peel the skin from the chiles, then discard membranes and seeds and cut chiles into fine dice. Remove husks from corn and discard. Carefully cut kernels from each cob, then transfer the corn to a medium bowl. Add diced chiles, zucchini, tomato, green onions, oregano, lime juice, oil, garlic, and salt. Makes 14 servings (3-1/2 cups).