1
Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 450 degrees. Wash and dry produce.
Halve, core, and thinly slice poblano crosswise into strips. Halve and peel onion; thinly slice one half. Finely chop remaining half until you have 2 TBSP. (For 4, thinly slice whole onion; finely chop a few slices until you have 3 TBSP.) Dice tomato.