Heat oil in a small pan over medium-low heat. Toast the peppers, stirring constantly, until fragrant (about 20 seconds). Remove the peppers immediately to prevent burning. Continue roasting the garlic, until golden brown. Remove the garlic and turn off the heat. Let the oil cool down completely. 

In a large molcajete, combine the toasted chiles, roasted garlic, and 1/2 teaspoon of salt. Using the pestle, mash the mixture into a smooth paste. Then, add the cooled oil to the molcajete and mix until well combined with the pestle. 

Add half of the onions, along with all of the lime juice, oregano, salt to taste, and pepper to the molcajete. Mix until the onions are fully coated with the salsa. Let them stand for a few minutes, allowing them to soften and shrink. Then, add the remaining onions and mix until they're also evenly coated with the salsa.

Taste and adjust the seasoning as needed, adding more salt or lime juice to taste.