Saute onions and garlic about 4 minutes, until onions are translucent.
Add cumin, cayenne pepper, chili flakes and dried oregano. Make sure to mix well and cook for 2-3 minutes.
Add black beans, chicken and green chilies. Salt and pepper to taste. Cook for around 2 minutes until incorporated and heated through.
Add chicken stock a little at a time, just to moisten the mixture. You may not need to use the entire 1/4 Cup. You want to make sure that the mixture is moist but not soupy. Simmer for about 5-7 minutes.
Take mixture off burner and let cool to room temperature.
Add cheese and mix thoroughly.
Roll out dough onto floured surface.
Cut 4" circles out of the dough (I like to use a medium sized cereal bowl to cut the circles, but you can make yours smaller or larger).
Fill the middle of each circle with about 1.5 - 2 Tbl of the mixture. Don't overfill. Fold each circle in half (sealing in the mixture) and crimp the ends with a fork to close the dough.
Brush tops with egg yolks and sprinkle with chili powder.