Preheat the oven to 400 degrees F.
In a large mixing bowl, toss together the Brussels sprouts, pancetta, olive oil, garlic, and some salt and pepper. Spread the sprouts in an even layer on a sheet tray or roasting pan.
Place in the oven and roast, stirring once halfway through, until the sprouts are tender and slightly browned, 18 to 20 minutes.
Remove from the oven and transfer to a serving dish. Toss with the lemon juice and zest. Garnish with shaved Parmesan.