Preheat the oven to 500 degrees F. Place the bread on a rimmed baking sheet and toast for 5 minutes. Flip bread and toast until golden and crispy, about 2 minutes.
In the meantime, cut the tomatoes in half and grate the cut side of the tomato on the large holes of a box grater into a shallow bowl. Grate in the garlic clove and add the vinegar, olive oil and 1/2 teaspoon kosher salt. Stir to combine.
Spoon the tomato mixture on top of each slice of bread, making sure to cover the toast completely from edge to edge. Drizzle the toast with a generous amount of olive oil and sprinkle with flaky salt.