Prepare your slow cooker with cooking spray.
In slow cooker add diced tomatoes, tomato paste, onions, garlic, Italian seasoning, salt and pepper. Stir until combined.
Add beef rolling around to coat. Cover and cook on low until beef is tender, 7-8 hours.
Remove beef from slow cooker and remove any string.
Using 2 forks shred or chunk into bite sized pieces. I find that different cuts of meat shred differently so do not hesitate to cut the meat into small chunks as necessary.
Transfer to a mixing bowl.
Add 2-4 cups of the sauce to the beef and toss to coat. I love sauces and gravy so I tend to add in more sauce than Ken does when he makes this. The amount of sauce is up to you.
Serve wrapped in a tortilla with green onions, sour cream and any other toppings if desired. Enjoy!