Heat butter in a medium skillet over medium-high heat. Add onion and bell pepper and sauté for 4-5 minutes. Make sure that fish has been patted dry thoroughly with paper towels. In a large bowl, add cilantro, fish, pepper flakes, garlic and cooled onion/pepper from pan. Sprinkle flour, breadcrumbs and lemon pepper over while tossing, making sure to coat fish evenly. Fold in mayonnaise and egg whites. Take some of the mixture and form into a ball, about 3 inches in diameter. If it holds together, you're in business. If it's too dry and flaky, add some more breadcrumbs. It should be moist, but not soggy. Form mixture into 8 equal sized patties.
Add enough oil to just cover the bottom of a large skillet and heat over medium heat. When oil is hot, add cakes and cook until medium brown on one side, about 5 - 6 minutes. Carefully flip over and brown other sides, about 5 minutes more. When cakes are just cooked, remove from pan and top with Chipotle Mayonnaise.