In a deep frying pan, over a high dry heat, add the tomatoes and char them all over until blistered and softened (approx. 5 - 10 mins). Add in the garlic cloves for the last 2 mins. Once done, remove to a bowl.
In the same pan, add a little oil and the tomato paste and fry until the puree turns a darker red - approx. 2 -3 mins. Add a little stock to loosen it up for a minute before adding all the stock in and then the tomatoes and garlic. Simmer for 15 - 20 mins until it reduces a little. Season and add a squeeze of lemon before adding in the orzo and cook for 5 - 7 mins (or until done).