Based on a recipe we learned at the Sante Fe School of Cooking.

Starting with a basic green chili sauce:

15 roasted green chili, mild  
3 hot roasted green chili
3/4 cup oil
4 Tbsp flour
3 cups chopped yellow onion
1/4 cup minced garlic
1 tbsp ground coriander
3 cups chicken stock
1/4 cup finely minced cilatro
salt

Saute the onion in the oil until soft. Add garlic until fragrant. Add flour and stir well. Add remaining stuff except salt and heat to a boil. Simmer 15 minutes and salt to taste. Remove from heat.

4 pounds cubed lamb leg or shoulder
4 tbsp oil

Heat oil to shimmering and brown lamb. Add lamb and chili mixture to crockpot and cook 6 hours on low. Thicken to taste with Mexican Roux:

1 cup corn flour
1/4 cup oil
juice of 2 limes

Heat oil to shimmering and stir in corn flour. Cook until smooth paste and then add lime juice. Add to stew until it is the desired thickness and adjust flavors.