Microwave the chopped pancetta or bacon on high for 3 minutes. Drain the drippings, and set the crispy pancetta aside.
In a large frying pan, heat the olive oil over medium heat. Cook onion in oil until soft. Add the garlic, and cook a minute more. Stir in chopped greens, and season with salt to taste (be conservative at this point – you can always add more!). Partially cover the pan, and cook until the greens begin to wilt. Stir in crispy pancetta and cannellini beans. Cook partially covered for 5 more minutes, until the flavors have combined and the greens are tender. Serve with polenta or cornbread.