Fry pancetta in a large pan for about 5 minutes on medium heat until browned. Remove pancetta from pan and set aside.
Heat oil in the pan and cook the onions and garlic on medium high heat for about 3 minutes, then reduce heat to medium low, cover and cook for 15 minutes, stirring occasionally, until onions are soft and start to caramelize.
Add the broth to the pan and bring to a boil. Once boiling, reduce heat and simmer, covered, for about 10 minutes. Add pancetta and season with salt and pepper to taste.
While the soup simmers, toast slices of ciabatta on both sides.
Pour soup into individual oven safe bowls, top with toasted ciabatta and cheese. Broil until cheese is melted approximately 3 to 5 minutes.