Using a wide pan over medium heat, add 1 tbsp of oil. Once the pan is hot, begin by adding the diced onion and cook for 2-3 mins.
Add in the minced garlic and cook for another minute. (At this point, you can add a little more oil if necessary)
Next, add in the diced capsicum and sauté for another 3-5 minutes for them to be soft and slightly charred. Transfer to a plate and set aside.
Using the same pan, add the other tablespoon of oil into the pan. Once hot, add the chicken and 2 tablespoons of taco seasoning and stir occasionally till cooked. (If you are using raw chicken, you will need to cook for about 4-6 minutes)
Once the chicken is cooked, add back the onions and capsicums and stir to mix well. The filling is now done, remove from the pan and set aside.