In a large bowl, mix all ingredients for the marinade. Pour half the marinade into a sealed plastic bag. Set the chicken in the bag and marinate at a fresh temperature all night.
Set aside marinades left at fresh in a glass jar (will be use for chicken sauce).
Preheat barbecue at medium high heat. Over hot and oiled grill, set chicken legs and cook with indirect cooking (see chef's tips) for 25 to 30 minutes, until completely cooked.
Brush frequently with marinades left for the first 20 minutes of cooking. Set potatoes and leeks over aluminum paper.
Spray olive oil, salt and pepper. Fold aluminium paper to form a papillote. Set over barbecue grill and cook for 15 to 20 minutes, until tenderness. Once cooking finished, transfer papillote in a large bowl.
Pour lemon juice and cool down. Once vegetables are cooled down, add arugula salad. Set chicken legs into plates. Garnish with marinade set aside. Divide salad into plates and spread with crumbled goat cheese.
For a perfect cooking, turn on only one side of your gaz barbecue at medium heat. If you have a charcoal barbecue, set embers over one side only. Cook chicken over th grill which isn't over flames to create indirect cooking. This small detail will avoid chicken to burn.