Heat a large pot with 1 tablespoon of oil. Fry the diced onion and garlic until lightly browned. Add tomato paste, ginger and curry paste and roast for another minute. Stir constantly. Deglaze with vegetable soup. Add turmeric, sweet potato, carrots and salt. Bring to the boil once, then switch back to a low setting and put the lid on the pot. Simmer for about 20 minutes until the vegetables are soft.