Brush onion slices with 1 tablespoon olive oil. Grill, without grill lid, over high heat (400° to 500°) 6 to 8 minutes or until tender. Cut each slice in half; set aside.
Grill poblano chile peppers and red bell pepper, without grill lid, over high heat (400° to 500°) 6 to 10 minutes or until skins are blistered and blackened.
Place peppers in a heavy-duty zip-top bag; seal, and let stand 10 minutes to loosen skins. Peel peppers; remove and discard seeds. Cut peppers into 1/2-inch strips.
Combine onion, peppers, 1 teaspoon oil, and remaining ingredients; toss gently.