Wash the lettuce leaves, pat dry and pluck into bite-sized pieces. Quarter the tomatoes and remove the hard stem. Drain the peppers, black olives and feta. Halve the peppers crosswise. Cut the feta into cubes or crumble with your fingers. Put everything in a salad bowl and sprinkle the onion rings on top.
Prepare a dressing with olive oil, vinegar and salt and drizzle over the salad. Sprinkle with freshly ground black pepper to taste.