Step 1 Spray a large saucepan with cooking oil; set over high heat. Cook diced lamb, in batches, for 2 minutes, or until browned. Remove lamb and set aside.
Step 2 Return pan to medium heat and spray with oil again. Cook onion, carrot and celery, stirring occasionally, for 5–6 minutes, or until soft. Add curry paste; cook for 1–2 minutes, or until fragrant.
Step 3 Return reserved lamb to pan. Add diced tomato and lentils with 3 cups water; bring to the boil. Reduce heat to low, cover pan and simmer, stirring occasionally, for 1 hour, 15 minutes. Add sweet potato, cover pan and simmer, stirring occasionally, for another 20 minutes, or until lamb and sweet potato are tender.
Step 4 Stir silverbeet through curry; simmer, uncovered, for 5 more minutes, or until silverbeet wilts and curry is thick. Season with cracked black pepper.
Step 5 Microwave poppadoms according to packet instructions. Serve curry with poppadoms.