Heat the oven to 375°F/190°C.
On a sheet pan, toss the tomatoes, garlic, olive oil, oregano, and salt. Roast until softened and lightly blistered, about 15 minutes.
Spread pesto on one cut side of the baguette and layer with mozzarella. Drizzle the remaining olive oil over the other half and sprinkle with coarse salt.
Add the roasted tomatoes, arugula, and balsamic glaze. Close the sandwich, press gently, and slice.