Place tomatoes in a shallow serving dish. Arrange onion rings on top. Arrange green bell pepper rings on top of onions.
Combine olive oil, cider vinegar, garlic, parsley, salt, sugar, and black pepper in a jar. Close jar tightly and shake vigorously until dressing is well-mixed. Pour dressing over tomatoes, onions, and peppers. Refrigerate until flavors combine, about 2 hours.