In a large bowl, combine the tuna breadcrumbs and egg and stir lightly. Add the onion,celery,pimento(if using),lemon juice,horseradish,garlic,pepper and mix again. Form the mixture into four 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.
*If you want, you can refrigerate the patties once formed for a couple of minutes until they are set.