In a 3.5 quart saucepan, bring the broth and the poblano peppers to a boil over high heat. Partially cover the pan and reduce to a simmer. Allow to cook for 10 minutes at a simmer.
Carefully pour mixture into a food processor or blender and blend until you have a smooth puree.
Strain and press through a sieve into a clean bowl, discard remaining solids. You should have about 2 cups of liquid, if not, simply add some more chicken broth. Stir in salt to taste.
Using the same 3.5 quart pan, wipe the pan clean and add the oil over medium heat. Add the rice and onions, stirring to ensure that everything is evenly coated. Continue to cook until the onions get translucent, about 5 minutes, stirring frequently, making sure nothing sticks to the bottom or burns.
Add the garlic and cook for 1 minute, stirring constantly to prevent burning. At this point you can drizzle in a little more oil if you think it is too dry.
Quickly add the broth back to the pan, stirring once to make sure nothing is sticking to the bottom. Bring to a boil first, then reduce the flame to medium-low, or a light simmer, and cover. Cook for 15 minutes.
Turn off the heat and allow to stay covered for 5-10 minutes. Fluff with a fork before serving. Garnish with chopped cilantro if desired.