In a mini processor or food processor, finely grind the panko crumbs. Place it in a shallow bowl.
In a food processor, grind 1/3 of the shrimp until it is finely ground (about 15 pulses). Remove from food processor bowl. Add the remaining 2/3 of the shrimp to the bowl and coarsely grind (about 6 pulses). Don’t over pulse. You can hand chop any pieces that are too large.
In a small bowl, combine the lemon zest, scallions, mayonnaise, granulated garlic, celery salt, black pepper and cayenne pepper. Add the mixture to the ground shrimp and mix thoroughly.
Make 6 patties the size of a hamburg bun. Dredge each patty in the ground panko crumbs (pressing crumbs to adhere to the patties, making sure you get the sides as well).
Heat canola oil in a 12-inch nonstick pan over medium heat. Place all six shrimp patties in the pan. Cook for 6-8 minutes or until golden brown. Flip the patties and cook an additional 5-7 minutes. Turn the heat down if they start to brown too quickly. They need to reach an internal temperature of 145 degrees. Place on paper towel to drain.