Preheat the oven to 450°. Put a large pot of water on to boil. Toss the onions, carrots, zucchini and bell pepper with the oil and spread on 2 large baking sheets. Roast for 20 to 25 minutes, stirring several times, until caramelized and golden brown. Transfer to a bowl, add the garlic and toss well. Reduce the oven temperature to 425°.
Meanwhile, salt the boiling water, add the fusilli and cook, stirring occasionally, until al dente, about 11 minutes. Drain.
Add the pasta to the roasted vegetables along with the cream, tomatoes, parsley, Fontina and 1/4 cup of the Parmesan. Season with salt and pepper; stir well. Transfer to a 13-by-9-inch baking pan; top with the remaining 1/4 cup Parmesan. Bake for 15 to 20 minutes, or until bubbling and golden brown. Let the pasta rest for 5 minutes before serving.
The pasta can be assembled up to 8 hours in advance and refrigerated until baking time. Remove from the refrigerator when you turn the oven on and increase the baking time as necessary.