Add water and vinegar to a medium sized pan and add sugar, mustard seeds and garlic. Bring to boil and let the sugar dissolve.
Meanwhile slice tomatoes into bite sized pieces and add to a jar.
Pour vinegar mixture overtop until you fill up the jar. Let cool and then add to the fridge. Let sit overnight.
Preheat oven to 425°F
Remove crust from box, overwrap, & cardboard. Add pesto if adding, cheeses and then top with tomatoes. Bake for12-15 min. Enjoy!