In a small dry skillet, toast the cumin seeds over medium heat until lightly browned and fragrant, 1 to 2 minutes. Crush the seeds in a ceramic or marble mortar, then add the garlic and salt and grind to a paste.
Work in the Anaheim pepper and cilantro until smooth. Gradually add the olive oil and then the vinegar and 2tablespoons water. Season the sauce with additional salt if needed.
Pour into a small bowl, and let stand at room temperature for at least 2 and up to 5 hours before serving.