Preheat oven to 180 degrees Celsius.
Clean mushrooms by wiping with kitchen paper. Remove stalks from mushrooms.
Dice stalks and onion finely. Chop basil and spinach finely.
Roast pine nuts in a 180C oven, or under griller, until light brown. Chop, or process in a food processor. Dice sundried tomatoes.
Heat oil in a saucepan. Add onion and garlic and cook until onion is transparent. Add diced mushroom stalks and cook for a minute. Add the basil, spinach, salt and pepper. Cook briefly.
Remove from heat. Add the pine nuts, tomatoes, breadcrumbs and parmesan. Mix well.
Spoon mixture into mushroom caps and sprinkle extra parmesan on top.
Cook at 180C on a lightly greased oven tray for about 7 - 10 minutes (until heated through, but not mushy).