There's really nothing to it. Cut the tomato into wedges, arrange them around the plate, decorate with onion slices (yes, even for breakfast!), crumbled feta cheese (the fattier, the better), and olives. A drizzle of olive oil and a shake of salt and pepper, and you're done.
The hard part is really picking the tomatoes. Try to find some with taste. This kind of salad is not even worth making in winter with supermarket tomatoes.