Preheat grill to medium (375º- 425º). In a food processor, add red onion and bell pepper. Pulse 2-3 times to a coarse chop. Add salmon, panko, egg, lemon juice and zest, mustard, salt and pepper. Pulse about 8 - 10 times or until ingredients are fully incorporated. Salmon should not be too finely chopped.
Divide and shape into four equal-size patties (about 1 inch thick). Let rest 5 minutes. Place on grill and cook 4 minutes then flip. Grill 3-4 more minutes. Remove from grill, tent with aluminum foil and let rest 5 minutes.
To serve, place salmon patty on a Napa Cabbage leaf. Top with tomato slice, dollop of chive aioli and a second cabbage leaf.
For the chive aioli, in a medium bowl combine Greek yogurt, mayonnaise, lemon, chive, and sriracha. Season with salt and pepper to taste