Using a Microplane or citrus zester, grate the zest from the lemon into a jar; cut the lemon in half and squeeze in juice from half of the lemon, about 1 1/2 tablespoons. 

To a jar with a lid, add ¼ cup olive oil, garlic, Dijon mustard, salt and pepper. Close the jar and shake to mix

Heat the remaining 2 tablespoons olive oil in a large skillet over medium-high heat. Add the brussel sprouts and saute for 2-4 minutes, stirring only after a few are browned, but most are still tender-crisp. Add the hazelnuts to the skillet. Saute an additional 2 to 4 minutes. Add the vinaigrette from the jar. Saute an additional 2 minutes. Sprinkle with parmesan cheese, garnish with leftover hazelnuts, and serve.