Clean brussels sprouts, cut each in half.
Heat oil in large skillet over medium heat.
Saute pancetta until brown. Remove from heat and put on paper towel.
Cook onions in oil until softened.
Add brussels sprouts.
Cook 8 minutes each side until crisp on outside and soft on inside. Add garlic when you turn.
Reduce heat to low. Add lemon juice, salt, and pepper.
Transfer to bowl and top with parmesan cheese.