I think of this as a sheet pan sandwich recipe. You roast a bunch of mushrooms and scallions in a hot oven as your main components. And you whip up a simple poblano yogurt while those are roasting. Pile everything high on top of hearty slices of well-toasted bread, and you’re set.
The poblano yogurt is a key component here, but I totally understand if you want to skip out on it because of time, lack of poblanos, or you’re anti-chile. No problem, just about any flavor-forward yogurt slather will do in its place. You could simply crush a clove of garlic into some paste with a pinch of salt, and stir that in your favorite plain yogurt – also delicious. Or, whisk a tablespoon of harissa paste into your yogurt.