Place the yogurt and feta in the bowl of a food processor with the horseradish, lemon zest and juice, garlic, pepper and oregano. Process into a smooth sauce.
Layer the sub rolls with the meat topped with sliced tomato, onion, cucumber, hot peppers, parsley or cress. Slather the roll tops with lots of sauce and set into place. Cut the subs in half and serve.
Note: To serve with sliced steak rather than deli roast beef, bring a 1 1/2-pound piece of flank steak to room temperature and pat dry. Season the steak liberally with kosher salt or sea salt and coarse black pepper; drizzle with olive or vegetable oil. Cook for 10 minutes, turning once on a hot cast iron pan or griddle over medium-high heat. Let the meat rest, then slice very thinly on an angle against the grain.
This is one of many “Yum-o!” recipes – it’s good and good for you. To find out more about Yum-o!, Rachael’s nonprofit organization, visit
www.yum-o.org.