1. Heat the broiler to high. Arrange the poblanos on a sheet pan. Put them under the broiler and char until blackened on all sides, 10 to 12 minutes. Peppers can also be easily charred over a gas stovetop flame.
2. Put the peppers in a bowl and cover tightly with plastic wrap. Allow peppers to sit until cool enough to handle. Peel and seed the peppers.
3. Heat the olive oil in a skillet over medium-high heat. Add the jalapeño, onions and garlic and cook until the onions soften, about 5 minutes.