Heat oil in a large, heavy pot over medium-high heat
Add onion; sauté until translucent, about 3 minutes.
Add garlic, chile, oregano and cumin; sauté 1 minute.
Add water and beans.
Bring to boil.
Reduce heat to medium-low, cover, and simmer 1 hour.
Discard chile.
Add sugar, if using, and salt to bean mixture.
Simmer uncovered over medium heat until beans are tender and almost all liquid has evaporated, about 1 hour longer.
Remove from heat.
Using potato masher, coarsely mash most of the beans.
Season with additional salt, if desired.
(Can be prepared one day ahead. Cool slightly. Refrigerate, covered. Rewarm in nonstick saucepan over medium heat, stirring frequently.)