Whisk together the olive oil, lemon juice, oregano and salt and pepper. Add the red onion slices and let marinate while you prep the rest of the ingredients.
Slice or dice the green bell peppers, cucumbers, and tomatoes. Quarter or halve the kalamata olives. Tear or slice the lettuce.
Place the lettuce on top of the red onion mixture, add the rest of the salad ingredients and toss to combine.
Taste and adjust the seasoning.
Video
Notes
If you want to transport this salad, put the veggies on top of the onion mixture and then the lettuce. This will keep the lettuce from getting soggy. Just toss when you arrive. Can use red, yellow or orange bell peppers.