Arrange oven racks in middle and upper third positions; preheat the oven to 425 degrees F (220 degrees C). Line two 10x15-inch baking sheets with aluminum foil.

Toss tomatoes, bell peppers, onion, 1 tablespoon oil, balsamic vinegar, Italian seasoning, 1/8 teaspoon salt, and 1/8 teaspoon black pepper together in a large bowl; transfer to one of the prepared baking sheets.

Roast in the preheated oven for 30 minutes.

Meanwhile, drizzle bread slices with remaining 1 tablespoon olive oil; season with remaining 1/8 teaspoon each salt and black pepper. Arrange on the other prepared baking sheet.

Remove vegetables from the oven; push to one side of the baking sheet. Add sausage to exposed portion of the baking sheet.

Roast until vegetables are tender and sausage is heated through, 10 to 15 minutes, adding bread during the last 5 minutes. Sprinkle vegetables and sausage with oregano; serve with bread.