Place all ingredients for salad on a serving platter or in a bowl. Set aside.
Whisk all ingredients for dressing in a liquid measuring cup or place into a small container with a tight fitting lid (like a mason jar) and shake. Taste and adjust seasonings, if needed.
Before serving drizzle dressing over the top of the salad and toss gently. Enjoy immediately.
Spinach Substitutions: You could also make this salad with kale, arugula, or other salad greens. Each one will have a different taste and change the salad slightly.
Red Onions: If you don't want such a strong onion flavor in your salad, slice the red onions thin, soak in cold water for 10-15 minutes, then drain and dry on paper towels. They will still taste like onion, but not have such a punch.
Add Protein: This also makes a wonderful main-dish salad if you add some sauteed chicken, hard-boiled eggs, or steak.