Pan fry spring onions in 1 tbsp olive oil until soft and move to slow cooker, then pan fry olives until sealed on all sides and transfer to slow cooker. Add remaining olive oil to pan with flour and stir until a paste. Add tomato paste and half of stock, and stir until paste is fully dissolved in stock. Bring the liquid to a simmer, then transfer to slow cooker along with the remaining stock, ensuring the olives are covered. Cook on high for 4 hours.