1. Preheat oven to 400°F.
2. Scrub sweet potatoes and prick them in a few places with a fork. Place on a baking sheet and bake until soft all the way through, about 45 minutes to 1 hour.
3. Start beans and greens about 15 to 20 minutes before the sweet potatoes are done.
4. In wide, deep saucepan with cover, heat olive oil over low-moderate heat. Add shallots and cook until softened, about 5 minutes. Add garlic, rosemary sprig, and red pepper flakes and cook, stirring, for about a minute. Add beans and cook for 5 minutes, stirring occasionally. Add kale, cover the pan, and cook, stirring occasionally, for about 5 minutes or until kale is tender. Remove rosemary sprig, stir in lemon juice, and season to taste with salt and pepper.
5. To serve, slice each sweet potato lengthwise and push on the ends to open up middle. Spoon beans and greens into the center.