1. Soak pinto beans in 4 cups water overnight. Drain in a colander, and set aside.

2. Heat a grill, or turn on the broiler. Roast poblanos, turning, until completely charred, 5 1/2 minutes. Transfer to a medium bowl; cover tightly with plastic wrap. Let sit 10 minutes. Using your hands, rub off most of charred skin, rinsing hands frequently under cold running water. Slice poblanos in half, and remove seeds. Finely chop them.

3. Place pork in a medium bowl, and crumble achiote paste over top. Using your hands, rub paste into pork.

4. Place a saucepan over high heat. When hot, coat with cooking spray. Add pork. Cook, stirring occasionally, until browned, about 2 minutes. Transfer to a plate.

5. Reduce heat to medium. Add onions and garlic; cover. Cook, stirring, until onions have softened, about 6 minutes. Add cumin, bay leaf, and chiles; cook until mixture begins to stick to bottom of pan, about 2 minutes. Add vinegar, and cook, stirring, 30 seconds more.

6. Add chicken stock, pinto beans, and pork. Bring to a simmer, and cover. Cook 1 hour. Divide among four bowls, and serve.