PREHEAT oven to 350 degrees.
In a large bowl, COAT tomatillos, onion, and pepper with 1 Tablespoon of olive oil. PLACE tomatillos, onion, and pepper on a sheet pan. ROAST for 30 minutes until the tomatillos are soft and begin to brown slightly
REMOVE from oven and PLACE in a food processor or blender with the garlic, oregano, cumin, salt, lime juice, and vinegar. PUREE until smooth
TRANSFER to a medium saucepan, BRING to a BOIL over high heat. REDUCE heat to medium-low. SIMMER for approximately 10 minutes. ADD the cilantro. COOL and SERVE.