Meanwhile, heat a large frying pan on medium high with a teaspoon of olive oil.
Thinly slice the zucchini into quarters and then each quarter into thirds and place into the frying pan and add 1 portion of the finely chopped garlic therein.
Cook until browned, but still firm, approximately 2 minutes either side.
Remove from the heat and set aside.
Slice your focaccia in half and lay the zucchini on the top half, topping with the sliced gloucester cheese.
Place the butter into a small ramekin and melt for 25 seconds in the microwave. Add the wholegrain mustard and remaining finely chopped garlic, stirring to combine evenly.
Brush the garlic butter over the bottom half of your sandwich.
Place under the grill for 5 minutes or until the cheese has melted and the base is golden. Remove and set aside.
Meanwhile, add a little more olive oil into the frying pan and sprinkle the salt evenly over all the meatballs before placing into the frying pan.
Cook evenly on medium high heat for 3 minutes each side until it is cooked in the center.
Add the tomato sauce and continue cooking for a further minute until well heated.
Remove from the heat and carefully spoon the meatballs onto the base of your sandwich, spooning over a little tomato sauce and then topping with a slice of buffalo mozzarella.
Return to the oven for 2 minutes to melt.
Remove and allow to cool for 5 minutes.
Slice and serve.