On the top of a pizza box, use a ruler and a marker to draw lines parallel to three sides of the box—the left, right, and front (where the box opens)—one inch from each edge.
Using a box cutter or sharp scissors, cut along the three lines to make a flap in the lid of a pizza box. Fold the flap so that it stands up when the box lid is closed.
Cut aluminum foil to cover the inner side of the flap.
Glue the aluminum foil to the inner side of the flap, shiny side out.
Open the box and tape one sheet of plastic wrap across the inside of the opening you made when you cut the flap in the lid. Then close the box and tape the second sheet of plastic wrap across the same opening, on the outside. Tape very securely, to seal out air. You are making an airtight window for sunlight to enter the box.
Glue aluminum foil to the inside bottom of the pizza box, and then cover it with black construction paper. Black absorbs heat, and this black surface is where your food will be set to cook.
Place the box in a sunny spot, as directed by the leader. Adjust the flap to get the most sunlight possible to reflect off the aluminum foil and onto the plastic-covered window. Use a ruler, stick, or large straw to prop the flap where you want it. Optional: You can tilt the box by rolling a towel and placing it underneath the box.
To keep the paper liner clean, place the items you're cooking on a clear plastic or glass plate.
To remove food from the oven, lift the lid of the pizza box, and use oven mitts or potholders to remove the glass dish.