Cut 4 rectangles of heavy duty aluminum foil, each about the size of 1/2 a standard cookie sheet.

Combine first 5 ingredients (this can optionally be done in a blender).

Spray (or brush) the 4 large rectangles of aluminum foil with olive oil. Place chicken in center; brush with lemon/garlic mixture, then sprinkle with salt, pepper, and lightly dust with garlic powder.

Place a slice of onion and a sprig of parsley over each. Fold up aluminum into a loose, square packet and crimp edges tightly to seal well. Place in a shallow baking dish or on the grill.