I usually chop up a green pepper (I like big chunks - like about an inch),
half a purple onion,
2 or 3 tomatoes,
a cucumber (I peel the field cucumbers, but leave the English with skin on)
some kalamata olives,
and a hunk of feta cheese.
I never put lettuce in mine, becaues I always thought traditional Greek salad didn't have lettuce, and restaurants just added lettuce becuase it was cheap filler. But now I'm not so sure that is right because I went to a traditional Greek restaurant and there was lettuce in it... So who knows!
Then the dressing is:
3/4 cup olive oil (I always use less - more like 1/2 cup)
1/4 cup red wine vinegar (I use a little more than that)
1/2 tsp salt
1/2 tsp pepper
1/2 tsp oregano
2 or 3 cloves garlic
It makes a lot of dressing, so you can just put on what you'd like and save the rest for another time. I let it sit for a few hrs before serving, if I have the time.