If using turkey cutlets, cut into chunks and process in a food processor until ground.
Put into a medium mixing bowl.
In the same food processor bowl, process celery, onion, garlic, sage, marjoram, and sea salt. Process until onion and celery are finely chopped but not mushy.
Mix turkey with egg and fresh pepper.
Add celery mixture to turkey and mix until evenly combined.
Form turkey into six patties.
Heat oil in a large skillet over medium heat.
Cook turkey patties for about 5 minutes each side, or until cooked through and browned on the outside.
Remove patties from skillet.
Serve with sliced tomato and avocado. Pass around avocado mayonnaise and Dijon mustard as a topping.