Preheat the oven to 375 degrees F. CITRUS VINAIGRETTE: Combine all the ingredients in a jar or a tight-sealing plastic container. Shake to blend.
FRICO CUPS: Place a sheet of parchment paper on a baking sheet. Place 4 (1/4-cup) mounds of Parmesan cheese on the mat and gently tap down until each mound is flat and about 5 inches in diameter. Bake for 8 to 10 minutes, until golden and bubbly.
Meanwhile, invert a muffin pan onto the counter. Working quickly, use a thin spatula to transfer each of the Frico onto the inverted muffin tin (to form upside-down cups). Let cool until firm, about 5 minutes.
SALAD & ASSEMBLY: In a large bowl, combine all the spinach salad ingredients. Drizzle with the vinaigrette and toss to combine. Divide the salad among the Parmesan Frico Cups. Serve immediately.