Chicken with Whole-Grain Mustard & Zucchini in Packets

Preheat oven to 400 degrees F (or see Grill Variation, below).

To prepare packets, start with four 20- to 24-inch-long pieces of parchment paper or foil. Fold in half crosswise. With the parchment or foil folded, draw half a heart shape on one side as you would if you were making a Valentine. Use scissors to cut out the heart shape. Open up the heart.

Place a chicken breast on one side of each open heart fairly close to the crease and leaving at least a 1-inch border around the edges for folding and spread with mustard.

Toss zucchini, peppers, shallots, tomatoes, oil, thyme, salt and pepper in a large bowl. Place about 1 1/4 cups of the vegetable mixture on top of each piece of chicken.

Close the packet to cover the ingredients. Starting at the top, seal the packet by folding the edges together in a series of small, tight folds. Twist the tip of the packet and tuck it underneath to help keep the packet closed. Place the packets on a large rimmed baking sheet (packets may overlap slightly). Bake until the vegetables are tender and an instant-read thermometer inserted into the thickest part of the chicken registers 165 degrees F, about 25 minutes. (Carefully open one package to check for doneness--be cautious of the steam.) Let the packets rest unopened for 5 minutes before serving.

Grill Variation: Cooking in packets is great for the grill, but it's not safe to put parchment paper over an open flame, so use foil. To prepare packets for grilling, start with eight 20- to 24-inch-long pieces of foil. Layer two sheets for each of four packets (the double layers will help protect the contents from burning). Arrange the ingredients on one half of each double layer. Fold the foil over the ingredients and tightly seal the packets by crimping and folding the edges together. Grill over medium heat for 14 to 16 minutes, rotating the packets to another spot on the grill about halfway through to ensure even cooking.