In a large bowl, mix together the garlic-infused oil, spices (smoked paprika, cayenne pepper, oregano, chilli flakes, asafoetida), chopped tomatoes and mixed peppers.
Pour the mixture into the slow-cooker and place on a low heat setting.
Place the chicken fillets on top of the mixture and cover with a lid. Leave to slow cook for between 4-5 hours.
When you are ready to serve, prepare your fajita sides including gluten free wraps, soured cream or creme fraiche, grated cheddar cheese, lettuce and avocado.