Tear off four 18" by 12" pieces of heavy duty aluminum foil. Place 1 chicken breast in the center of each piece. Divide onion and garlic among pieces. Thinly slice lemon and divide among packets. Sprinkle each with salt and pepper. Divide frozen asparagus among packets. Top each packet with 2 tablespoons pesto and sprinkle with parmesan cheese.
Fold foil over chicken and vegetables and seal edges with a double fold. Place packets in zipperlock bag and freeze.
Thaw packets overnight in fridge. Prepare and preheat grill. Cook packets 4-6 inches from medium coals for 18-25 minutes or until chicken is thoroughly cooked and vegetables are tender, turning once.
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