Cook the pasta: Fill a large saucepan two-thirds full with water; bring to a boil. Liberally salt the water just before adding in the noodles. Cook the pasta according to the package instructions until al dente.
Make the vinaigrette: Blend all of the vinaigrette ingredients in a high-powered blender or food processor on high until mostly smooth. This yields 3/4 cup. It can be made 3 weeks in advance and stored covered in the fridge. If the vinaigrette hardens in the fridge, run under warm water and shake to combine.
Prepare the salad: Slice the vegetables. Set aside.
Assemble the dish: Return the cooked pasta to the pan along with 1/2 teaspoon of the salt. Pour in half the vinaigrette and stir together. Taste and add additional vinaigrette and salt as needed. Distribute the pasta evenly among the plates, and top with the spinach, onion, olives, and feta. The greens will wilt slightly from the warmth of the noodles.