Heat the olive oil in a large frying pan over a medium heat and brown the vegan meatballs. Remove to a bowl. Heat the olive oil in the pan and fry the red onion for 10-12 mins over a low heat until soft. Stir in the garlic and cook for 1 min. Add the chopped tomatoes. Cook for 5 mins, then return the meatballs to the pan and cook for 10-15 mins until the sauce has thickened and the meatballs are cooked. Stir in a handful of the basil. Cut the focaccia loaves into 8 slices by cutting each down the length, then through the middle. Spoon 4 meatballs over 4 slices along with some sauce. Scatter over some grated vegan hard cheese and sandwich with the remaining slices. Best served on the day but will keep chilled for 24 hrs.