Season your brisket well with 1 tbsp fajita seasoning. Pop your oil in the saute pot over a medium heat. Brown the brisket pieces all over. Set aside. To the residual oil, add your peppers and onions. Fry for a couple of minutes until translucent.
Add the brisket back to the pot along with the garlic, remaining fajita seasoning and beef stock (it should come about half way up the beef). Cook for 6 1/2 hours on low. Remove the brisket and shred with forks. Pour over the cooking liquor. Place a spoonful in a tortilla then top with the toppings of your choice!!