Step 1: Preparing the Cornish Hens or Chickens: Unwrap Cornish hens or chicken. Remove giblets from cavity; rinse and pat dry. Place Cornish hens or chicken on cutting board breast-side-up with open cavity facing you. Using poultry shears or kitchen scissors, cut through the entire length of the breast area. Flatten Cornish hen by pressing firmly down with both hands to so it resembles one large flat section. (Or ask the butcher where you shop to split and flatten the Cornish hens or chicken for you.)
Step 2: Prepare Marinade: Select a Marinade and mix all ingredients.
Place Cornish hens or chicken in large resealable plastic bag or glass baking dish. Add Marinade; turn to coat Cornish hens or chicken evenly. Seal bag or cover dish. Refrigerate at least 2 hours or overnight for best flavor.
Step 3: Prepare Bricks and Grill: One brick will be needed for each Cornish hen and two for the chicken. If necessary, rinse bricks before using. Wrap each brick in 2 layers of heavy duty aluminum foil. Ensure that grilling surface is clean and ready to use. If using nonstick cooking spray, apply only to a cold grilling surface.
Step 4: Grilling: Preheat grill 5 minutes over medium-high heat. Reduce heat to medium or medium-low (target cooking temperature is 325°F to 350°F). Remove Cornish hens from Marinade. Place skin-side down on preheated grill. Carefully and quickly position bricks on top of Cornish hens; close lid. Discard any remaining Marinade. Grill Cornish hens 20 to 25 minutes or chicken 40 to 50 minutes or until cooked through, turning halfway through cooking time. Remove bricks using oven mitt, turn Cornish hens or chicken and place bricks back on top to finish cooking.