Place the poblanos, tomatillos, onions and garlic on a baking sheet and put them in the oven on the middle rack.
Roast for 20 minutes or until the vegetables are charred. You may wish to turn them once during cooking.
Place the poblanos, tomatillios, onions, garlic, cilantro, salt, pepper, cumin, oregano and lime juice in a blender or food processer and pulse into a chunky salsa verde.
If using, add half of the jalapeno and taste for spice. Add more as needed.
Serve salsa verde warm or chilled.
Refrigerate and use for up to 5 days, or freeze any leftovers and use for up to 4 months.