Pre-heat the oven to 375 degrees F. Place the cornbread cubes in a large bowl and drizzle with 2 tablespoons of the olive oil. Toss evenly to coat the bread cubes. Spread the cubes in a single layer on a sheet tray and bake until lightly browned and toasted, about 10-12 minutes. Return the toasted cornbread to the bowl and add the tomatoes, cucumbers and onions, if using.