1. Preheat oven to 250°.
2. Cut off mushroom stems and rinse thoroughly. In a large serving bowl, whisk 1 tablespoon oil and lemon juice. Marinate mushroom caps in the mixture for 20 minutes (or until you complete the next steps).
3. In a sauce pan, heat 1 tablespoon of olive oil on medium heat. Add onions and garlic. Cook 3 to 5 minutes, stirring occasionally.
4. Add parsley, artichoke hearts, basil, spinach, and sun-dried tomatoes. Cook for 12 minutes. Cool slightly. Stir in Parmesan cheese.
5. Remove mushrooms from marinade. Place in a big dish. Scoop make sure into mushroom caps. Place in oven for 15 minutes.