Prep the chiles: Snap off stems, shake out seeds. Toast pods 30 sec per side in a dry skillet, then cover with hot water 5 min to soften.
Blend the sauce: Drain chiles; blend with onion, garlic, broth, vinegar, cumin, oregano, 1 tsp salt until velvety.
Load the slow cooker: Add cubed pork, season with pepper, pour sauce over, stir to coat.
Cook low & slow: LOW 7–8 h, or HIGH 4 h. Pork should shred with a fork and sauce will thicken.
Finish & serve: Taste for salt, thin with a splash of broth if needed, scatter cilantro. Spoon into bowls or over cauliflower rice.