Preheat oven to 400 degrees F and line a baking sheet with parchment paper.
Cut a sweet potato in half lengthwise and place one half flat side down on the parchment paper.
Bake for about 40 minutes or until the sweet potato half is soft when tested with a fork.
Scoop out the inside of the sweet potato half into a bowl and add the tuna, egg, breadcrumbs, green onion, carrot, lemon zest, parsley, and black pepper.
Mix until combined, lightly breaking up the tuna while mixing.
Place olive oil in a frying pan over medium heat.
Shape about 1/4 cup of the tuna mixture into a small round cake and cook in the heated frying pan for about 2-3 minutes on each side or until golden brown.
Repeat with the rest of the tuna mixture.