Prep charcoal grill with medium-hot coals or heat gas grill to medium-high heat.
In a large bowl, stir together olive oil, lime zest, lime juice, 1 teaspoon of the chili powder, 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper. Add corn, peppers, onion and garlic; stir to coat.
Using 12-inch-wide heavy-duty aluminum foil, cut 4 pieces 32 inches long; fold each piece in half to make a 16 x 12-inch rectangle. Generously coat foil pieces with nonstick cooking spray.
Evenly divide mixture on one half of each foil piece. Sprinkle tilapia with remaining 1/2 teaspoon chili powder, 1/2 teaspoon salt and 1/4 teaspoon pepper. Place seasoned fillets on top of vegetables in foil.
Fold second half of foil over fish and vegetables. Tightly seal sides and front edges, leaving space for steam to build. Place foil packets on grill rack; grill 20 minutes. Carefully open packets; transfer contents to 4 serving plates. Sprinkle with cilantro.