To make the sauce, place all of the ingredients into a small pot with 100ml of water over a low heat and gently cook for 15-20 minutes, ensuring it does not boil. Cool to room temperature then pour into a blender and blend with a pinch of salt until very smooth. This can be made up to week in advance and stored in an airtight container.
Heat a BBQ or grill pan over a high heat. Place the onion and capsicum a teaspoon of oil and salt and pepper in a bowl and toss to coat vegetable well. Place on the grill and cook for 5-6 minutes or until slightly charred. Place in a bowl and keep warm.
Massage oil over chicken and season with salt. Sear strips for 3-4 or until cooked through.
Warm the tortillas in a dry pan over a medium heat for 1 minute on each side. Keep warm in a clean tea towel.
Toss chicken and charred vegetables, a good squeeze of lime and an extra splash of olive oil. Serve along with the sauce, avocado and warm tortillas.
