Cut the onion and Brussels into thin slices. Alternatively, run the Brussels sprouts through a food processor equipped with a slicing blade. In a skillet with a lid, heat the olive oil over medium-low heat. Add onions and cook until translucent; 6 to 8 minutes. Add in the Brussels sprouts and cook for another 2-3 minutes. Add in 2 tablespoons water, cover, and let cook until Brussels sprouts are tender, 6-8 minutes. Remove lid, stir, and continue to cook until any liquid is gone, 2-3 minutes.

In a bowl, toss together brussels sprouts, einkorn, and sesame seeds. In a separate bowl, whisk together the remaining ingredients. Pour over the salad and toss until well combined.