Preheat oven to 350°F. Lightly spray a 9×13-inch baking dish with nonstick cooking spray
Heat 2 tablespoons olive oil in a 12-inch skillet over medium heat. Add chopped onion and green bell pepper and sauté until translucent (5-7 minutes). Stir in 1 tablespoon minced garlic and cook 1-2 minutes until fragrant
Add 1 pound ground beef to the skillet. Cook and crumble until no pink remains, then drain excess grease
Stir in 1 1/2 teaspoons salt, 3/4 teaspoon black pepper, 1 tablespoon Italian seasoning, and 1 1/2 jars spaghetti sauce. Set aside while preparing alfredo sauce
Boil spaghetti in salted water per package instructions, then drain completely
In a separate pan, melt 1/2 cup butter. Add 4 cloves garlic and sauté 1 minute on low heat. Stir in 1 tablespoon flour and cook 1-2 minutes
Gradually whisk in 2 cups heavy cream, simmering until thickened. Remove from heat and stir in 1 1/2 cups grated parmesan
In a large bowl, combine cooked spaghetti, meat sauce, and half the alfredo sauce. Transfer to prepared baking dish
Top with remaining alfredo sauce, shredded mozzarella, and a sprinkle of parmesan. Bake 25 minutes until golden and bubbly