In a large bowl add the chicken thighs, peppers, red onions, spices and rapeseed oil. Marinate for 30 minutes in the fridge.
Fry the chicken thighs on a medium heat in a non-stick pan for 8 minutes on each side or until golden brown. Remove from the pan and shred the chicken using either a hand blender or two forks.
In the same pan, add the peppers and the onions and fry on a medium heat for 5 minutes.
Add the passata and water to the peppers and onions. Cook for 6-7 minutes on a medium low heat, stirring every so often. Add the shredded chicken into the pan and cook for a further 3 minutes.
Dip each side of each taco shell into the shredded chicken and set aside.