Spread the onion, summer squash, zucchini, eggplant, and red bell pepper out onto two baking sheets with rims; drizzle vegetables with olive oil, and sprinkle with salt and black pepper.
Roast the vegetables in the preheated oven until soft and starting to brown, 20 to 25 minutes; stir and turn over vegetables after about 10 minutes of baking. Decrease oven temperature to 375 degrees F (190 degrees C).
While vegetables are roasting, fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the penne, and return to a boil. Cook the pasta uncovered, stirring occasionally, until the pasta has cooked through, but is still firm to the bite, about 11 minutes.
Drain well in a colander set in the sink.
Grease a 2-quart casserole dish. In a saucepan, mix together the Alfredo sauce with chicken broth, and bring to a boil.
Pour the sauce mixture into a large bowl, and stir in the roasted vegetables, penne pasta, 1/4 cup of Parmesan cheese, and 1/4 cup of mozzarella cheese until thoroughly combined. Spoon the mixture into the prepared casserole dish; sprinkle top evenly with breadcrumbs. Cover the dish.
Bake in the hot oven until mixture is bubbling, about 30 minutes.
Remove cover, and sprinkle top of casserole with remaining 1/4 cup of Parmesan and 1/4 cup of mozzarella cheeses; return to oven, and bake until the top is lightly browned and the cheese has melted, 5 to 10 more minutes.
