Tear off 4 (18- x 12-inch) heavy-duty aluminum foil sheets.
Place a fillet in center of each foil sheet; sprinkle evenly with salt, pepper, and Cajun seasoning. Top evenly with squash and bell pepper; dot with butter. Sprinkle evenly with lime rind and remaining ingredients.
Bring up 2 sides of each foil sheet, and double fold with about 1-inch-wide folds. Double fold each end to form a packet, leaving room for heat circulation inside packet. Place packets on a baking sheet.
Grill, covered with grill lid, over medium-high heat (350° to 400°) 15 minutes or until fish flakes easily.