Generously oil the bottom and sides of a 9 x 13 inch (23 x 33 cm) pan with extra virgin olive oil. Use gravity to allow the dough to naturally stretch until it reaches the edge of the pan. If you notice the dough pulling back to center, allow it to rest in the sheet pan for an additional 10 minutes, then continue stretching.
Use your fingertips to make indentations on top of the focaccia dough. Crush whole peeled tomatoes in your hands over the focaccia dough. Allow the juice and tomatoes to spread across the dough. If there is any leftover tomato juice, pour it over the focaccia dough. Evenly pour the olive oil on top of the dimpled focaccia. Sprinkle Maldon sea salt flakes on top.
Cover the pan with plastic wrap, and allow to proof in a warm (75°F - 80°F or 24°C - 27°C), draft-free place until tripled in size, about 60 minutes.
Place oven rack in an upper middle slot. Heat oven to 430°F (220°C).
Carefully remove plastic wrap from pan without knocking any air out of the bread dough. Bake for 25 - 30 minutes until golden brown and crispy on the top. Place focaccia on a cooling rack, and cover with a tea towel. Allow focaccia to cool to room temperature before removing from the pan and slicing into 24 individual pieces.
To serve, heat oven to 350°F (180°C). Line a baking sheet with parchment paper, and place focaccia slices on top. Bake for 18 -20 minutes until warmed through and crunchy on the outside. Top each slice of focaccia with a slice of mozzarella, basil leaf, a drizzle of garlic olive oil, and more Maldon sea salt flakes.