Preheat the oven to 350 degrees F.
In a large bowl, combine the tuna, bread crumbs, and egg, and stir lightly. Add the onion, celery, pimento (if using), lemon juice, horseradish, garlic, and pepper, and mix again. Form the mixture into 4 patties. Heat the oil in a nonstick skillet over medium heat and cook the patties, covered, until golden brown. Carefully flip the patties and cook the other side for 5 minutes. Finish baking in the oven until golden brown.