Preheat oven to 350 degrees F. Spray a 13 x 9 inch baking dish.
Heat the oil in a large dutch oven. Add the onions, peppers, mushrooms, garlic, zucchini, and broccoli. Sautee vegetables 6 minutes.
In a large mixing bowl, stir together the egg, italian blend cheese, mascarpone cheese, and butter.
Bring a large saucepan of salted water to a boil. Break the spaghetti into half, add to the water and cook for 10 minutes. Drain water. Add spaghetti to the bowl with egg and cheese, toss to coat the spaghetti.
Spread 1/2 cup pasta sauce on the bottom of baking dish. Add spaghetti to dish. Top with the sautéed vegetables. Pour remaining pasta sauce over the vegetables/spaghetti. Sprinkle mozzarella cheese over the sauce.
Bake for 30-35 minutes or until cheese is melted and mixture is bubbly.
Cut into squares and serve warm.