Heat olive oil in a skillet over medium heat and cook onions until tender and caramelized-- about 10 minutes. Add in chicken and ranch seasoning, stir and cook for 1 minute.
Stir in hot sauce, butter and yogurt. Use more hot sauce and less yogurt if you like it spicy and the opposite if you like it milder.
Heat the chicken thoroughly and spoon into warm corn tortillas. Top with blue cheese crumbles, shredded cabbage, cilantro, and sour cream to serve.