Tilapia, a firm-fleshed white fish with a mild taste, takes well to a number of cooking options, including being wrapped in aluminum foil before grilling or baking. Wrapping tilapia — whole or in fillets — creates an enclosed cooking space, which lets the fish — and any vegetables you include in the package — steam in its own juices. This produces a moist, flavorful fish with the bonus of an easy cleanup -- just throw away the foil.
Before cooking defrosted tilapia, season the fish with spices and fresh herbs. Options include plain pepper and salt, or more complicated combinations, such as pesto or a mix of Asian spices, like fresh grated ginger, minced garlic and soy sauce. If you are cooking a whole tilapia, stuff the cavity of the fish with fresh herbs, and cut diagonal slashes along the fish, rubbing the seasonings directly onto the flesh. Tilapia fillets can be cooked from frozen in foil packets. In this case, you cannot marinate your fish beforehand. Add the spices and herbs directly to the packet. Avoid using high-acid foods, such as citrus and tomato, as the high cooking temperatures can cause the acids to react with the aluminum foil, leaving black specks on your fish.
To make the foil packet, tear off a large piece of foil, and lay it with the longer edge toward you. It does not matter if you use the shiny or dull side of the foil. Brush the center of the foil with a thin layer of cooking oil. If you are cooking vegetables with your tilapia, scatter them over the oiled area, and place your tilapia on top. You can make the foil packet any number of ways, but be sure that the ingredients are fully enclosed, with no chance for steam or juices to escape during cooking. One way of wrapping the fish tightly is to bring the two long edges together and fold them. Repeat this pleating twice, so the edges stay securely closed. Fold the two shorter ends up by pleating them in 1-inch folds. Leave a 1- to 2-inch space between the fish and the foil.
You can cook your foil tilapia packets on the grill or in the oven. If you are cooking fillets from frozen, a longer cooking time will be needed. On a grill, use a medium to low heat to prevent your fish or vegetables from burning and sticking to the foil. In a 350 degree Fahrenheit oven, a packet containing 1 defrosted tilapia fillet and 1 cup of raw, cut vegetables will cook in approximately 25 minutes. You can check doneness by unwrapping the foil packets — be careful of escaping steam, which can easily burn you. The tilapia is done when it turns opaque and flakes easily with a fork.
Serve the foil packets individually if you like, cutting a slit in the foil and pushing the edges apart. This is a fun and relaxed way of serving your fish. Warn guests about escaping steam though, so they do not accidentally scald themselves. You can also take the tilapia and vegetables out of each packet and transfer them directly to a plate for a more elegant presentation. Whole tilapia can be filleted before serving, or it can be brought to the table whole on a platter. If you are using lemon juice or other acidic seasonings, add them just before serving.