Whisk marinade ingredients together to combine. Pour half the marinade into a shallow dish to marinade the chicken fillets for two hours if time allows. Refrigerate the reserved untouched marinade to use as a dressing.
Heat about one teaspoon of oil in a grill pan or skillet over medium-high heat and grill chicken fillets on each side until golden, crispy and cooked through. (Grill in batches to prevent excess water being released.) Once chicken is cooked, set aside and allow to rest.
Wipe pan over with paper towel; drizzle with another teaspoon of oil and fry pepper and onion strips until cooked to your liking.
Slice chicken into strips and prepare salad with leaves, avocado slices, peppers, onion strips and chicken. Drizzle with remaining marinade/dressing and serve with (optional) extra cilantro leaves and sour cream.