Preheat the oven to 400ºF. Line 2 baking sheets with parchment or waxed paper.
In a large mixing bowl, toss the potatoes, carrots, tomatoes, and onion with 2 tablespoons of the olive oil. Season with salt and pepper. Put the vegetables on the prepared baking sheets. Roast the vegetables until golden brown and very tender, 20 to 25 minutes.
Toss the bread cubes with the remaining 2 tablespoons olive oil. Season with salt and pepper. Place them on a baking sheet and bake until golden, 3 to 4 minutes.
Arrange the roasted vegetables and bread on a platter and serve with the fondue, dunking them in the cheese with a skewer or fondue fork.
Yield: about 4 servings