Step 1 Spray a large saucepan (that has a lid) with olive oil; set over medium heat. Add chicken in 2 batches; cook for 2–3 minutes, or until golden. Remove chicken from pan and set aside.
Step 2 Spray pan with olive oil again and return to medium heat. Add onion and celery; cook, stirring occasionally, for 5 minutes, or until onion softens. Add curry paste to pan; cook, stirring, for 1–2 minutes, or until fragrant. Add sweet potato cubes to pan and cook for 1 more minute.
Step 3 Add lentils and diced tomatoes to pan with 2 cups water; bring to the boil. Reduce heat and simmer (pan partially covered with lid) for 18–20 minutes, or until sweet potato is just tender.
Step 4 Return reserved chicken to pan with sliced zucchini and simmer for another 5 minutes, or until zucchini is just tender. Season curry with cracked black pepper.
Step 5 Divide steamed quinoa (or rice) among serving bowls, garnish with coriander leaves and serve.