Lay the tomatoes out on a paper towel and sprinkle with a few pinches kosher salt so that some moisture drains out of them.
Line a baking sheet with parchment and place the round of pie dough on top (if using homemade dough, roll it out into a round that is 11- to 12-inches in diameter).
Brush the edges of the dough with the egg wash, then sprinkle with the mozzarella, garlic and fresh basil. Top with the tomatoes. Fold over the edges and pleat. Brush the outside edges with the egg wash and sprinkle with flaky salt and pepper.
Bake the galette until the edges are golden brown, 35 to 45 minutes. Finish with more basil and enjoy!