Add the oil to a large pot and fry the onion, garlic and celery over medium heat until translucent but not browned.
Add the chopped tomatoes and fry for another 3 minutes.
Add the carrots, mushrooms and baby marrows.
Add the warmed stock and bring up to a simmer.
Add the tomato puree, sugar and balsamic vinegar and season with salt and pepper.
Let the soup simmer for 15 minutes, stirring occasionally.
If some of the liquid has cooked away, top-up the level of liquid in the pot with just-boiled water.
Increase the heat until the soup is bubbling well, add the pasta shapes and stir frequently as the pasta will quickly stick to the bottom of the pot otherwise.
Cook until the pasta is al dente, add frozen peas and reduce the heat.
Check the seasoning, adding salt and pepper if necessary. You could also add some just-boiled water again if the soup is too thick.
Add the tin of baked beans just before serving, mixing carefully.
Serve with a sprinkling of fresh chopped parsley and crusty bread.