Combine the mashed potato, drained tuna, eggs, garlic powder, parmesan cheese, chopped parsley, mayonnaise, salt, black pepper, and panko bread crumbs in a large bowl. Mix until well combined, then use your hands or a scoop to form the mixture into balls, about 3-4 tablespoons each.
1 yellow potato, 3 cans tuna, 2 eggs, 1 teaspoon garlic powder, ½ cup freshly grated parmesan cheese, 1 tablespoon chopped parsley, 3 tablespoon mayonnaise, 1 teaspoon salt, Freshly ground black pepper, 1 cup panko bread crumbs