Coat slow-cooker bowl with nonstick cooking spray.
Heat oil in a large nonstick skillet over medium-high heat. Season beef with 1/4 tsp each of the salt and pepper and add to skillet. Sauté 3 minutes per side.
Transfer beef to slow cooker. Layer in onion, potatoes and carrots. In a medium bowl, whisk together coconut milk, curry, soy sauce, ginger, garlic powder and cayenne. Pour over beef and vegetables in slow cooker.
Cover and cook on HIGH for 6 hours or LOW for 8 hours. Gently stir in remaining 1/4 tsp salt. Serve over flatbread wedges with parsley, yogurt and lime, if desired.