Preheat a gas or charcoal grill. Brush the poblanos, onions, and jalapeño with 1 tablespoon oil. Grill 5 to 7 minutes, turning halfway through, until softened with nice grill marks. Remove and set aside.
Cut the avocados in half and remove the pit, leaving the skin on. Brush the cut side of the avocados with the remaining oil, and grill for 30 seconds. Rotate ¼ turn and grill another 30 seconds. Remove and set aside.
Split the jalapeño and poblano peppers lengthwise, remove the stems, veins, and seeds. Chop the peppers and onions, and add to a large mixing bowl.
Scoop the flesh of the avocados into the bowl with the peppers and onions. Add the lime juice, salt, and cumin, and mix to combine. Fold in the tomatoes and cilantro. Serve immediately.