The pancetta is optional, so you can make this meatless if you wish!
In a large skillet, heat the oil, three turns of the pan, over medium to medium-high. Add the pancetta, if using, and cook, stirring often, until the fat begins to render and the pancetta is lightly crispy, about 3 minutes.
Add the onion, garlic, and rosemary; season with salt and pepper. Cook until the onion softens, about 5 minutes. Add the beans and cook, stirring often, until heated through, about 1 minute. Add the kale leaves and nutmeg. Stir until the kale wilts, 2 to 3 minutes. Stir in the lemon juice; season the salad.