Tilapia is easy to cook in foil on the grill and you don't even have to thaw it out first. A very mild-flavored whitefish, tilapia fillets cook up relatively fast, however you choose to cook them. If they're frozen, you can thaw them on the grill, open the packet of foil and add seasoning, then continue cooking as usual. Adding seasoning is particularly important for tilapia; the mild flavor can be bland on its own. Fresh aromatics such as garlic, onions and herbs can be added to the packet once the fish has thawed to add intense flavor.
Prepare your grill for medium-high heat, about 400 degrees Fahrenheit. Brush the grill grate with canola oil.
Remove your frozen tilapia from its packaging and rinse under cold water to remove any ice that may have formed, then pat dry with a paper towel.
Tear a sheet of aluminum foil large enough to fold in half and still fully cover your tilapia fillet. Fold the sheet in half and lay the fillet in the center.
Drizzle olive oil on both sides of the frozen fillet, then fold opposite sides of the aluminum foil over top of the fish, folding the excess over to seal. Roll up the open ends as well to create a sealed packet.
Place the packet on the hot grill with the seam side down. Cook for about 8 to 10 minutes, then remove from the heat using tongs and check the fish, which should be significantly thawed.
Sprinkle the tilapia with salt and pepper, to your taste. You can also add minced garlic, chopped onions and fresh herbs for more flavor. Reseal the packet and place it, seam-side up, back on the grill.
Cook the tilapia for another 8 to 10 minutes, or until the tilapia is white, firm and flakes easily with a fork. Fish should be cooked to 145 degrees Fahrenheit to ensure it is safe to eat, according to FoodSafety.gov. A meat thermometer will help you determine the correct temperature.