Heat a medium saucepan over medium heat. Swirl 1 tablespoon vegetable oil to coat the pan.
Saute the remaining onion and garlic cloves, until soft 3 to 5 minutes.
Add in a pinch of chili powder and the remaining cumin, sugar, and salt. Stir to coat, cooking 30 seconds, until fragrant.
Add the green chiles, mixing to combine.
Simmer for 2 minutes, as things start to thicken, add a splash of chicken broth and deglaze the pan, scraping up any browned bits.
Add the remainder of the chicken broth and bring to a simmer.
Reduce the heat to medium-low and allow to thicken 8 to 10 minutes.
Remove from heat and add in the cilantro.
Working in batches, when cool enough to handle, pulse in a blender until smooth.
Reheat in a saucepan when ready to use.
The sauce can be made a day or two ahead and stored in an airtight container if desired.