When ready to serve, combine the spinach and arugula mixture in a large bowl. Add the shaved Brussels sprouts, cooled sweet potatoes, farro, quinoa, apple slices, red onion, and toasted pumpkin seeds.
Drizzle the top with some of the well-whisked vinaigrette, to taste; toss to coat evenly.
Serve immediately with freshly cracked black pepper on top. Enjoy.