For salad, heat grill to medium.
In large bowl, toss onion slice, zucchini and peppers in olive oil. Season with salt and pepper.
Grill vegetables until just cooked, about 3 minutes.
After grilling, separate onion slice into rings, keeping larger rings for sandwich and tossing smaller ones with remaining vegetables.
Cool briefly and toss with lemon or lime juice. Add a little more olive oil if desired.
For sandwich, increase heat on one side of grill to high and turn other side off. Preheat 5 minutes.
In small bowl, combine duck meat with barbecue sauce.
Take 1 slice of bread and coat one side with ½ of butter.
Mix mayo, lime juice and Szechwan pepper and spread ½ of mixture on unbuttered side of bread.
Place 1 slice of cheese on mayo side of bread, top with reserved onion rings, chopped cilantro, duck and other slice of cheese.
Spread remaining mayo on other slice of bread and place on top of sandwich.
Brush remaining butter atop bread. Press down on sandwich to compress a bit.
Place sandwich on unlit side of barbecue and press down with a spatula to compress. Close lid.
Heat 3-4 minutes or until bread is crispy and cheese is beginning to melt.
Flip sandwich carefully and press down. Close lid again and heat another 3-4 minutes.
Remove from grill, cut in ½ and serve with some grilled vegetables and a zucchini flower.

Smoked turkey or chicken may be used instead of duck.

Canadian Swiss or Raclette may be used instead of Gouda.