To make garlic lemon aioli: In small bowl, combine yogurt, lemon juice, garlic powder and salt. Cover and refrigerate until serving time.
To make tuna-carrot cakes: In medium bowl, combine 1/2 cup corn flake crumbs, yogurt, carrot, onion and relish. Add tuna; mix well.
Place remaining corn flake crumbs on piece of wax paper. Shape tuna mixture into eight 3/4-inch thick patties. Lightly coat both sides of patties with crumbs.
In large nonstick skillet, heat oil over medium-high heat. Cook patties in hot oil 4-6 minutes, or until golden brown, turning once. Stir aioli. Spoon dollops on patties. Garnish with additional onion, if desired.