In medium bowl toss lamb cubes with 1 Tbsp. of the curry powder and set aside.
Heat butter and olive oil in heavy skillet and add lamb cubes. Brown on all sides, about 4 minutes, and remove to a 4-6 quart crockpot.
Add onions and remaining 1 Tbsp. curry powder to skillet; cook and stir until onions are crisp tender. Stir in flour and cook and stir until bubbly. Add 2 cups water and stir until thickened. Pour this mixture into slow cooker. Add remaining ingredients except coconut milk, lemon juice, and rice. Cover and cook on LOW for 8-9 hours until all ingredients are tender. Stir in coconut milk and lemon juice and serve over hot cooked rice. Serves 6