• Prep mushrooms- Start by snapping off the stems, and use a spoon to scoop the gills out of four portobello mushrooms. Wash, then pat gently dry. Brush mushrooms on all sides with olive oil, and arrange on a sheet pan.
  
• Fill mushrooms- Spoon ¼ cup of marinara sauce into each mushroom. Mix together ricotta, spinach, basil and egg, then divide it evenly between four mushrooms. Sprinkle tops with shredded mozzarella cheese.
  
• Bake- Place in a 400°F oven, and bake for 20 minutes, or until mushrooms are dark brown and tender. You do not want the mushrooms to get completely soft, as they will collapse and all the lasagna fillings will spill out.
  

Freezing for later

• Prepare and bake portobello mushrooms as indicated above. Cool completely, then wrap each mushroom in foil. Place foil-wrapped mushrooms in a meal prep container, reusable silicone bag or plastic freezer bag.Freeze for up to 3 months.
  

To bake from frozen

• Heat oven to 350°F. Unwrap the mushrooms, and flatten out foil. Arrange frozen mushrooms in a 9 x 9 inch baking dish, then cover the dish with the foil (or use a reusable silicone lid).
• Bake for 40- 50 minutes, or until cheese is bubbly and mushrooms are heated through. You may want to remove the lid for the last 10 minutes to help liquid evaporate.