Place chicken pieces into a bowl. Pour in half of the olive oil. Add lemon juice, minced garlic, chopped cilantro, oregano, paprika, and chilli powder. Season with salt and pepper. Mix well and let chill in the fridge for 20 minutes.
Heat remaining oil in a frying pan. Add marinated chicken pieces and cook for 7-10 minutes or until golden.
Peel and slice avocado.
Take lettuce leaves and load them with chicken pieces. Put some avocado slices on top. Drizzle with sour cream. Sprinkle with some more chopped cilantro and black pepper, and enjoy!