1. Preheat oven to 425 degrees Fahrenheit. Line and grease a hard (real) baking sheet. Add mushrooms and onions. Season with salt and spray with cooking spray. Bake for 25 minutes.
2. Meanwhile, whisk together dressing ingredients (you’ll need to let it sit for a few minutes to allow the cubes to thaw).
3. To serve, add greens to a bowl. Top with mushrooms and onions and creamy pesto dressing.