Preheat oven to 180°

Remove stems from mushrooms, and finely chop stems to measure 1/4 cup

Discard remaining stems

Combine 1/4 cup chopped stems, onion, and next 6 ingredients (through garlic)

Heat a large nonstick skillet over medium heat

coat pan with cooking spray

Add onion mixture to pan; cook 10 minutes or until vegetables are tender

Combine onion mixture and bread in a large bowl, tossing to combine

Slowly add broth to bread mixture, tossing to coat

Add feta and toss gently

Remove brown gills from the undersides of mushroom caps using a spoon and discard gills

Place mushrooms, stem side up, on a baking sheet coated with cooking spray

Brush mushrooms evenly with 1 tablespoon vinaigrette

Sprinkle Parmesan and black pepper evenly over mushrooms

top each with 1/2 cup bread mixture

Bake at 180°C for 25 minutes or until mushrooms are tender

Combine remaining 2 tablespoons vinaigrette and greens, tossing gently

Place 1 cup greens on each of 4 plates

top each serving with 1 mushroom.