Use a sharp knife to remove the stems and damaged outer leaves of the sprouts. Slice each sprout into thin (⅛th inch) slices, or use a food processor to shred them.
Heat the olive oil in a skillet then add the pancetta. Cook until almost crispy, then add the chopped onions and minced garlic. Sauté until translucent but not browned.
Add the shredded Brussels sprouts to the skillet and sauté until crisp tender.
Add lemon zest, a generous squeeze of lemon juice, sea salt and pepper to taste, then serve hot.
Notes
If pressed for time, you can use pre-shredded Brussels sprouts.