Steam the green beans for about 5 minutes or until tender crisp. I like to leave them whole but they can be used cut in one inch lengths; set aside.
In a small bowl mix together yogurt, feta cheese, parmesan cheese & pepper.
Taste and adjust seasoning; do not salt, the cheese & olives are quite salty; set aside.
In a small casserole or au gratin dish, layer green beans and tomato slices, starting with green beans, as you go cover each tomato layer with a thin coat of the yogurt mixture. Finish the layers with the yogurt mixture. Scatter the chopped olives over all.
The dish can be served cold as a salad at this point or if you prefer a hot side dish bake in 400°F oven for approximately 20 minutes until heated through, either way it is delicious.