For the lamb shank ragu: Preheat the oven to 350 degrees F. Heat a large Dutch oven over high heat. Sprinkle the lamb shanks generously with salt and pepper.
Add olive oil to coat the hot pot and sear all sides of the lamb shanks until golden brown, about 5 minutes per side. Remove from the Dutch oven and set aside. Add another tablespoon olive oil to the pot, if needed, and saute the carrots, celery, garlic and onions until golden brown and fragrant. Next, add the mustard powder and red pepper flakes and cook 1 minute to release their flavor. Add the tomato paste and cook 1 minute to brown.
Lower the heat to medium, deglaze with the red wine and cook until reduced by one-quarter. Return the lamb shanks to the pot followed by the chicken broth, rosemary, thyme and tomatoes. The lamb shanks should be covered three-quarters of the way up by the liquid. Season with salt and pepper and bring to a simmer. Cover, transfer to the oven and cook until the lamb shanks are just about to fall off the bone, about 2 hours.
For the cheesy gnudi: Bring a large pot of salted water to a full simmer over high heat. Combine the ricotta, fontina, Parmesan, 1/2 of the lemon zest, eggs and a pinch salt and pepper together in a large bowl. Mix with a spatula until smooth. Slowly add in the flour until a soft dough comes together (it may take more or less flour). It may be best to mix with your hands at this point so that you can feel the wetness and texture. You want to add just enough flour until the dough stops being "wet."
Divide the dough into 3 equal portions. On a floured surface, roll each portion into a rope about 12 inches long and 1/2-inch thick. Cut the ropes into 1-inch pieces, using a knife.
Working in batches to avoid overcrowding, add the gnudi to the pot of simmering water and cook just until they rise to the top. Remove the gnudi using a slotted spoon and transfer to a sheet tray. Repeat the process until all the gnudi is cooked.
For assembly: Remove the lamb shanks from the pot, transfer to a large bowl and let cool until you can handle them. Strain the sauce and stir in the whole-grain mustard. Shred the lamb meat and toss with the strained sauce. Return the lamb and strained sauce back to the Dutch oven to keep warm.
Melt the butter in a large saute pan over medium-low heat until golden brown and nutty. Add in the gnudi and saute, 1 to 2 minutes. Add the peas and asparagus and continue to cook, 1 to 2 minutes longer. Season the mixture with salt and pepper, then toss in the mint and remaining lemon zest.
Toss the pea shoots with olive oil, lemon juice, salt and pepper. Plate the gnudi with the lamb ragu on top and garnish with the fresh pea shoot salad.