Here is a simple recipe I adapted from a restaurant, now closed, on the Country Club Plaza in Kansas City.
Richly flavored dark bread
Black olives, cut up
Slice onions and tomatoes; soak in balsamic vinegar for one to two hours.
Place feta cheese, olives, and soaked tomatoes and onions between two slices of bread.
Drizzle olive oil in 300 degree frying pan.
Fry sandwiches on both sides until dark like toasted cheese sandwiches.
you can panini it but I prefer not to.