Slice tomatoes and peppers and set aside. Slice the red onion and separate the rings.
Using a large bowl with a lid, layer the tomatoes, green pepper and onion until all vegetables are used. Shake the bottled dressing and pour desired amount over the vegetables. Refrigerate for 2 to 3 hours or, for best results, overnight.
Before serving, shake bowl to ensure all vegetables are coated with the dressing.