Toss the beef with the flour, curry powder, allspice, 1 teaspoon salt and 1/2 teaspoon pepper in a medium bowl; transfer the beef to a 6-quart slow cooker. Add the sweet potatoes and bell pepper to the bowl and toss to coat with any remaining flour mixture. Spread over the beef. Whisk the coconut milk and ginger in a bowl until combined; pour over the vegetables.
Cover the slow cooker and cook on low, 7 hours. Uncover, stir well and let stand 10 minutes. Skim off any fat from the top. Stir in the lime juice and season with salt. Serve over rice; top with scallions and serve with lime wedges.