Once the mixture comes to a full boil, turn off the heat and allow the chiles to sit in the hot water for at least 10 minutes while you prepare the rest of the sauce.
Add the chopped onion, garlic, dried oregano, cumin seed, achiote paste, orange juice, white vinegar, pure maple syrup, and sea salt to a high-powered blender.
Remove the stems and seeds from the chiles and place them in the blender along with 2 cups of the liquid used to boil them. Blend on high until the sauce is smooth.