In a medium mixing bowl combine the spicy mustard, yellow mustard, garlic, salt, and pepper. whisk to combine. Add in the balsamic, mix again. Drizzle in the olive oil while whisking. Mix until smooth.
In a large bowl, combine the spinach, chopped walnuts, feta, pomegranate seeds. Toss to combine, drizzle the mustard vinaigrette over the top, toss again to combine and serve.