Put a perforated vegetable grilling rack, or a couple of layers of aluminum foil in a pinch, over the fire to heat. Make the marinade/sauce: Grate the lemon zest into a small bowl. Add the garlic, 1/4 C cilantro, mustard, and 1/4 C olive oil, then squeeze the lemon juice in as well. Quickly whisk to emulsify, taste, and add salt and pepper to taste.