Brush the pitas with the olive oil and cut each into 6 triangles. Spread the triangles in a single layer on a baking sheet, sprinkle with salt and cook until they are crunchy, 10 to 13 minutes (turn the sheet halfway through cooking if necessary).
In a bowl, combine the Greek yogurt, dill and lemon juice. Add the black olives, cucumbers, tomatoes and red onions and mix to combine.
Spoon the yogurt sauce over the pita chips and sprinkle with feta.