Cook the orzo according to package directions. Drain and rinse with cool water to stop the cooking. Let it sit in the colander while you finish the vegetables and the dressing.
Meanwhile, heat 2 tablespoons of the olive oil in a large skillet with a lid over medium-high heat. Add the broccoli and red onion, season with salt and pepper, and saute for about 2 minutes until the vegetables just start to soften. Add ¼ cup water, place the lid on the pan, and continue cooking for another 2 to 3 minutes until the broccoli is bright green and crisp-tender.
While the broccoli is cooking, in a large bowl, combine the remaining 2 tablespoons olive oil, lemon juice and zest, vinegar, and salt and pepper. Add the cooked broccoli and the olives, if using, and toss. Add the cooked orzo and toss again. Serve at room temperature.
Notes
Wasting broccoli by tossing the stems is a true shame. Often, recipes will call for broccoli florets, chopped or whole, which assumes you are either buying the broccoli crowns without their stems or you should find another use for the stems, or worse, toss them. There is no need for that — much of the stem is very usable.
All you need to do is cut off the stems, trim the dried woody bottom of the stem, and then peel the tough skin from the outside. The inside is perfect, crunchy but not fibrous. You can roughly chop it and then cook it with the rest of the chopped florets. It will be tender and just a bit crunchy, depending on how long you cook the broccoli.