Start heating a large pot of salted water for the gnocchi.  Defrost the spinach. 

While it heats, place the olive oil in a skillet over medium heat and add the pancetta.  Cook until it starts to turn golden, then remove with a slotted spoon. Add the garlic to the pan and cook briefly; it should not brown. Add the tomato sauce and sprig of basil. Cook for 5-10 minutes until the flavors blend. Season to taste with salt and pepper.

Cook the gnocchi in the boiling water and drain well. Place them in an oven proof dish. Add the pancetta, spinach and  tomato sauce. Mix lightly. Next tear pieces of mozzarella and arrange them on top of the gnocchi. Sprinkle the chopped basil over everything.

Place the dish in a 350 F oven for about 20 minutes, until the sauce is bubbly and the cheese is melted.