Bring a large pot of water to a rolling boil. Cook pasta until al dente, according to package directions. Drain and keep hot.
In a large, deep skillet over medium-high heat, add the butter. Once melted and hot, add the sliced onion, green pepper, and mushrooms. Add the salt and black pepper to taste. SauteĢ the veggies until they are softened and golden brown, about 10 minutes. Add the garlic and stir; cook for 30-60 seconds or until fragrant. Remove the skillet from the heat and stir in the red wine vinegar. Pour the peppers and onions into the colander with the pasta.
In the same skillet, add the ground beef and Italian seasoning. Crumble the beef with a wooden spoon as you cook until it is completely browned through. Drain off any fat. Add the pasta and veggies from the colandar into the skillet with the beef.
Meanwhile, in the same pot used to cook the pasta, make the sauce. Add the butter and heat to medium heat. Let the butter melt and then whisk in the flour, whisking constantly for 1-2 minutes. Gradually add the milk and beef stock, whisking continuously for 1-2 minutes.
Allow the sauce to thicken for about 5 minutes, stirring every minute or so. Add the Italian cheese blend; stir until melted and smooth. Turn off the heat and pour the sauce over skillet with the beef, peppers, onions and pasta. Toss to make sure everything is well combined. Serve with chopped parsley, if desired.