Wash and dry the spinach.
Toast the pecans or walnuts in a dry skillet or oven.
Thinly slice the red onion. Soak in cold water for milder flavor if desired.
Prepare the vinaigrette by whisking together olive oil, balsamic vinegar, Dijon mustard, honey, salt, and pepper.
Combine the spinach, cranberries, pecans, feta cheese, pomegranate seeds, and red onion in a large bowl.
Dress the salad with the vinaigrette just before serving.