In a large bowl, combine salmon, mashed potatoes, bread crumbs, egg white, celery, green onion, mayonnaise, mustard, lemon zest, pepper and cayenne pepper. Form into 8 cakes.
In a large frying pan, heat canola oil over medium heat. Cook salmon cakes, turning over once, until golden and just cooked through, about 6 – 7 minutes.
Lemon Yogurt Sauce
In a small bowl combine yogurt, lemon juice and zest. Serve salmon cakes with sauce.