In a bowl, mix together the oil and spices. Add the vegetables and mix well.
Spread over a heavy baking sheet, then roast for 30 mins until tender.
Spoon into a food processor or liquidiser with half the stock and process until smooth. Pour into a pan with the remaining stock, season, then heat until barely simmering.
Remove from the heat and stir in the lemon juice. Garnish with cumin seeds.