Remove any innards from the Whole Chicken (3.5 pound) and prepare to spatchcock (I use kitchen shears and a boning or utility knife). Lay the bird breast side down on your work surface.
Locate the back bone. Starting at the thigh end, cut along both sides of the back bone to remove it, cutting through the ribs. I start with my kitchen shears then use my boning knife to get through the bones.
Once removed, lay the bird breast side up. Press down to flatten (you will hear a crack).
In a small bowl, mix the Honey Dijon Mustard (1/2 cup), Lemon (1), Garlic (3 clove), Fresh Parsley (2 tablespoon), and Ground Black Pepper (1/2 teaspoon). Add a splash of Olive Oil (to taste) if your mixture is too thick.
Brush the marinade on both sides of the chicken until fully covered, making sure to get under the skin. Marinate covered in the fridge for 6 hours or overnight.
Before grilling, allow the chicken to come to room temperature for at least 30 minutes to 1 hour.
Set the grill for indirect grilling. For a gas grill, heat one side of the grill to high while the other side remains off. For a charcoal grill, move the hot coals to one side of the grate.
Once hot, brush both sides of the chicken with olive oil and season with Sea Salt (to taste). Tuck in the wings and place the chicken breast side up on the indirect side of the grill (the side that is not turned on or lit).
Cover and grill for 45 minutes, or until the internal temperature reaches 155 degrees F (68 degrees C).
Take the chicken off of the grill and rest for 10 minutes. Transfer breast side down to the direct side of the grill (over the flame) and allow to char for a few minutes, or until temperature reaches 165 degrees F (74 degrees C).
Rest for a few more minutes, then serve alongside a honey mustard vinaigrette.