Thinly slice the green onion and sauté it in a skillet until soft. Add the chicken, season with salt, pepper, and a little ground cumin. Cook everything together over low heat until the chicken is cooked through.

Meanwhile, make the sauce: In a blender, combine the jalapeño, lime juice, chopped avocado (save a few slices for garnish), parsley, cilantro stems, and garlic. Blend until smooth and creamy.

Once the chicken and onion are cooked and golden, transfer them to a large bowl. Mix with the sauce and use this mixture to fill the tacos.