Pat lamb shanks dry and season generously with salt and pepper.

Heat olive oil in a large Dutch oven or oven-safe pot over medium-high heat. Sear lamb shanks on all sides until deeply browned, about 3-4 minutes per side. Remove lamb and set aside.

Add chopped onion to the pot and cook until softened, about 5-7 minutes. Add minced garlic and grated ginger, cooking for another minute until fragrant.

Stir in diced tomatoes, beef broth, peanut butter, soy sauce, rice vinegar, and red pepper flakes (if using). Bring the sauce to a simmer, whisking until the peanut butter is fully incorporated.

Return lamb shanks to the pot, ensuring they are mostly submerged in the sauce. If needed, add more broth or water.

Cover the pot tightly and transfer to a preheated oven at 325°F (160°C). Braise for 2.5 to 3 hours, or until the lamb is fork-tender and practically falling off the bone.

While lamb braises, prepare the gremolata: combine chopped parsley, lemon zest, and minced garlic in a small bowl. Set aside.

Cook white rice according to package directions; typically this means cooking for 15-20 minutes until rice absorbs liquid and is tender.

Once lamb is done, carefully remove shanks from the pot. Skim any excess fat from the sauce. Taste the sauce and adjust seasonings if necessary.

To serve, place a portion of cooked rice on a plate, top with a braised lamb shank and a generous ladle of peanut sauce. Sprinkle with gremolata before serving.