Heat the oil in a large, heavy-bottomed pot or a Dutch oven over a medium-high heat. Add the pancetta if using and cook, stirring occasionally until it begins to brown, about 5-7 minutes. Add the onion and cook until softened, about 8-10 minutes.

Make a little space in the pan and add a bit more olive oil. Add the garlic to the oil and stir for a minute. Add the bay leaf, canned tomatoes with the juices, scraping up the bits from the bottom of the pan. Season with pinch of salt and pepper. Let the tomatoes cook down for about 5 minutes and then add the beans, cheese rind and stock or water. Bring the soup to a simmer, adding more water or stock if needed. Add the kale leaves and the fregola and let the soup simmer for about 20-30 minutes. The pasta will cook in the broth.