Soak cannellini beans in a large bowl of cold water for at least 4 hours, up to overnight. Drain.
Pat lamb shanks dry; season with ground black pepper and dust with flour. Heat oil in pressure cooker over medium-high heat. Cook lamb shanks one at a time, turning to brown on all sides, about 10 minutes per shank. Transfer to a plate and set aside.
Cook and stir shallots, carrots, celery, and garlic in the oil left in pressure cooker until shallots are golden brown, about 15 minutes. Add rosemary and red wine; cook for 2 minutes, scraping up any browned bits from the bottom of the pan. Add drained beans, beef broth, and water; season to taste with more black pepper. Return the lamb shanks to the pot.
Seal the pressure cooker lid; bring cooker to full pressure according to manufacturer's instructions. Cook for 35 minutes. Turn off heat and allow the pressure to lower naturally, about 10 minutes.
Remove lid; stir in tomato paste, salt, lemon zest, and half of the chopped parsley.
Spoon bean and vegetable mixture into large shallow bowls; top with lamb shank meat and sauce. Sprinkle servings with remaining parsley.
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Be sure to avoid adding salt or tomatoes until after the beans have cooked. If you can't find low sodium beef broth, just use water so that the beans have a chance to cook through.