Refrigerate the sauce tightly covered until you’re ready (this can be done a day ahead).
Place chopped salmon in a food processor with onions, bell pepper, and garlic.
Pulse the salmon several times, scraping down the sides as pulse until the salmon is coarsely ground.
Add the rest of the burger ingredients – eggs, parsley, breadcrumbs, Cajun seasoning, salt, and pepper. Pulse until thoroughly combined.
Chill salmon mixture for an hour. Form four patties from equally-sized balls. Chill until ready to use. Perfect salmon burgers!
Clean grates, oil, preheat. Grill until charred on one side, flip, cook 4-6 min. Spread bun with aioli, add spinach, patty, tomato, onion