Cut tops off tomatoes. Gently scoop out pulp and seeds. Pat tomato with a paper towel to reduce moisture.
In a medium bowl, mix together cucumbers, green pepper and onion. Add olives whole or cut first.
In a separate bowl, whisk together vinegar, oil and seasoning. Pour over vegetables. Fold in feta.
Fill tomatoes with a slotted spoon. Chill before serving.