Mix together the fajita spiced mix and set to one side in a bowl. Why not make up a few batches to store in the cupboard for next time?
Add the garlic, peppers and onion into the slow cooker.
Add the fajita spice mix, stock and tomato puree. Mix everything together well.
Add the chicken breasts (whole) mix together gently ensuring the chicken is completely coated. Try to ensure most of the veggies are on top of the chicken.
Cover with the lid and cook for 3 hours on high or 4 hours on low. (Remove the lid for the last hour)
Remove the chicken breasts from the cooker, place onto a cutting board and slice into strips. Put these back into the slow cooker and mix everything together. [If you find there is still far too much liquid you can pop your slow cooker pan on the hob and boil off some of the liquid]
Serve and enjoy.