Soak the pinto beans in water overnight in a large mixing bowl.
Drain the beans and set aside.
In a dutch oven or other large vessel put the oil, onions, bacon, garlic and green chilies and cook over medium or medium-high heat until the onions are transparent and the edges of the onion have very lightly browned. Stir in the cumin powder.
Add the beans and 6 cups water. Increase heat to high, bring liquid to a boil, decrease heat to medium or medium-low and cook until the beans are very tender, adding more water as needed. Add salt and black pepper to taste.
I like to serve these beans in ramekins. They make a nice side dish to any Mexican meal.