In a food processor, blend onions and celery until very finely chopped.
In a large saucepan, heat oil and scrape in onion and celery. Sauté gently for 10 minutes, stirring every now and then to prevent sticking.
Meanwhile, put tomatoes, carrots, garlic, parsley, and chili in food processor. Blend until smooth.
After 10 minutes, increase heat, add spice blend to onions and celery and stir through for 30 seconds. Reduce heat to low and pour in tomato mixture. Stir through, and then add hot stock, red lentils, chickpeas, sweet potato, and tomato pureé.
Bring to a boil, and then reduce heat and gently simmer for 45 minutes, stirring occasionally.
Serve with lemon wedges and parsley