Ingredient Incidentals

• Cleaning arugula leaves is a crucial step. Swish several handfuls of them in a large bowl of cold water. If the greens are especially gritty, you may need to do this more than once. After you've drained and patted the arugula, tear the leaves into pieces, or chop them roughly. Fish fillets won't need much preparation before going into the packets. For extra flavor, however, you may opt to marinade the fish in olive oil, lemon juice and seasonings for about 30 minutes.

Packet Prep

• To enclose each arugula and fish serving, you have the option of using either aluminum foil or parchment paper. Because aluminum foil is more easily manipulated, a packet made from a rectangle of foil requires fewer steps. Fold a length of aluminum foil in half to create a crease, then lay it flat. The paper packet starts with a rectangle that is then folded in half and cut into a half-heart shape so that the paper looks like a heart when unfolded. This shape works well for folding the parchment around food.

Fishy Fabrications

• Before you set the food into the packets, it helps to butter or oil the inside of the center-creased rectangles, leaving the edges free for easier crimping. The food itself should be placed next to the crease in the center of the packet. A serving size of about 1/2-cup arugula leaves is about right for holding the fish. Once the fish is placed over the bed of greens, add optional toppings, such as lemon slices, a pat of butter or a drizzle of oil.

Steaming Seafood

• Sealing the packets tightly is the key to creating the trapped, hot air that gently steams the fish and the greens. The best way to do this with either foil or paper is to fold the other half of the packet over the fish and arugula. Fold the edges tightly by using a crimping motion similar to sealing a pie closed. Two packets should fit on one baking sheet. The sheet or sheets go into a 375 degree oven and cook for about 15 minutes. Make sure the fish flesh is opaque and flakes easily before serving.