Preheat the oven to 425°F and line a rimmed baking sheet with foil. Spray with cooking spray.
Cut the peppers in half lengthwise and scrape out the seeds. Place on the prepared pan, cut side down. Spray lightly with a little more cooking spray. Roast for 10-15 minutes or until the peppers have softened and they are starting to brown around the cut edges. Remove from the pan and place cut side up on a piece of parchment or another baking sheet. Let cool.
Fill the peppers with hummus, sprinkle with a little za’atar, and top with pimento pieces.