Preheat the oven to 425 degrees and place the poblano peppers on a baking sheet.
When the oven is preheated, place the baking sheet in the oven and roast the poblanos, rotating once or twice, for about 20-25 minutes or until tender and charred on all sides. Let the poblanos cool slightly, then peel the skins off and cut into strips.
Meanwhile, heat a medium saucepan over medium heat and add the butter. When the butter melts, add the onion and saute, stirring often, for about 5 minutes or until softened.
Add the cream cheese and sour cream to the saucepan and cook for another couple minutes to melt the cream cheese.
Add the poblano strips and shredded oaxaca to the saucepan. Stir to combine and cook for another couple minutes to melt the cheese. Season with salt, pepper, and dried oregano.