Prepare the dressing first. In the jar of your blender, combine all the ingredients except for the oil. Blend on high. While the blender is running, slowly add the oil in a steady stream. Refrigerate.

Cook the tortellini according to package directions. Meanwhile, combine the onions, tomatoes, cucumber, and olives, if using, in a large salad bowl.

When the pasta is done cooking, drain and rinse in cold water. When the pasta has cooled, toss it with the combined ingredients and then add the salad dressing a little at a time, and toss until combined. I generally use the whole batch of dressing, but you can start with some and go from there.