Heat oven to 400ºF. Place each chicken breast between two sheets of plastic wrap and pound to an even ½-thickness. Prepare four 20-by-30-inch pieces of parchment: fold in half and cut into a half-heart shape. Unfold and place chicken on one side of each paper.

In a bowl combine parsley, garlic, zest, salt and red-pepper flakes. Divide mixture among chicken breasts, covering the surface of each piece. Sprinkle with raisins and nuts.

Fold parchment over chicken breasts and pleat in 1-inch increments, folding edges over tightly to seal packet. Fold the last pleat underneath the packet. Place packets on a baking sheet; bake until packets are puffed and chicken is cooked through, 15 min.

Carefully transfer packets to plates, cut the paper across the top and tear to open.