Cut the bread slices in half lengthwise to make half-moons.
Heat the oven to 400ºF.
Drain the tomatoes and reserve the liquid for another use. Slice the tomatoes in half lengthwise and place them in a single layer on a rimmed baking sheet. Drizzle with 2 tablespoons of the oil and roast until lightly browned, about 20 minutes. Using a metal spatula, chop the tomatoes on the baking sheet (or remove them to a cutting board to chop). Use the spatula to scrape up the browned bits from the baking sheet and add them to the tomatoes. Transfer the tomatoes to a medium bowl and stir in the feta, oregano, garlic, salt, pepper, and 1 tablespoon of the remaining oil.
Brush one side of the bread with the remaining 1 tablespoon of oil. Toast the slices in the oven until very lightly browned, 2 minutes.
Spoon the tomato mixture evenly over the toast and sprinkle with the sesame seeds (if using). Serve immediately.
Tip: Make the filling ahead and keep it refrigerated for up to two days. Let it stand at room temperature while you toast the bread.