Heat oven to 200C/180C fan/gas 6 and wrap the tortillas in foil.
Mix the marinade ingredients together in a large bowl with a big pinch each of salt and pepper. Stir the chicken, onion, pepper and chilli, if using, into the marinade.
Heat a griddle pan until smoking hot and add the chicken and marinade to the pan. Keep everything moving over a high heat for about 5 mins using tongs until you get a nice charred effect. If your griddle pan is small you may need to do this in two batches. To check the chicken is cooked, find the thickest part and tear in half – if any part is still raw cook until done.
Put the tortillas in the oven to heat up and serve with the chicken, salad and salsa.