Cut cherry tomatoes in half. Take out the seeds and slice bell peppers and cucumber. (You can also choose to peel the cucumber of leave it with skin on.) Slice lettuce and onion thinly and either cut the olives or leave them whole. Combine the vegetables in a large mixing bowl.
Add feta cheese and olives and mix everything together.
Combine ingredients for the dressing in a jar with a lid or salad dressing shaker and shake well.
Pour the dressing all over the salad in a bowl and mix until the vegetables are all evenly coated.
Serve right away.
To make ahead: you can prepare the salad dressing ahead of time and store it in a glass jar with a lid in the refrigerator. You can also cut and combine all the vegetables in a bowl with feta cheese and olives, except for lettuce. Slice lettuce thinly and add it to the salad before serving. Mix the salad with dressing right before serving as well.