1.Combine one tbsp of curry paste and one tbsp of oil in a small bowl. Rub lamb with curry mixture then sprinkle with salt.
2.Cook lamb on heated oiled grill plate (or grill or barbecue) until browned and cooked as desired. Transfer to plate; cover, stand 5 minutes then slice thinly.
3.Meanwhile, heat remaining oil in a medium pan. Add onion, carrot and celery; stir over heat until vegetables are softened. Add garlic and remaining curry paste and stir over heat until fragrant.
4.Add stock and lentils; stir until hot. Remove from heat and add spinach and coriander. Toss until combined.