These were delicious! The stuffing would also make a great stuffing for pasta (I'm thinking stuffed shells might be in my future). Here's my advice on how much marinara sauce to actually use. You don't want the spinach mixture to be floating around in sauce but everything still needs to be moist. Start out with half a cup or so of sauce, mix it all together and add more if you need to.
If you're looking for a vegan option leave the cheese off. It's still good.
Stuffed Mushroom Marinara:
4 large portobello mushrooms, gills removed
2 tablespoons olive oil, plus some to drizzle
1 onion, chopped
2 carrots, chopped
2 cloves garlic, minced
1 box frozen, chopped spinach, thawed and squeezed as dry as possible
1 cup marinara sauce
1 teaspoon garlic powder
1 teaspoon onion powder
1 teaspoon dried oregano
salt and pepper
4 slices provolone cheese
Preheat oven to 400 degrees.
Heat a skillet over medium high heat. Add 1 tablespoon olive oil. When the oil is hot add the onion. Once the onion starts to brown add the garlic and carrots. Let everything cook for about a minute and add the spinach. Let the spinach mixture cook for an additional minute or so (I let them cook while I took the gills out of the mushrooms) and add the marinara sauce, salt, pepper, garlic powder, onion powder, and dried oregano. Stir to combine.
Brush each mushroom cap with a little olive oil and begin to stuff them.
Once each mushroom is as full as you'd like it to be place them on a baking sheet and place one slice of provolone cheese on top of each mushroom cap. Bake for 15-20 minutes, until the cheese is nice and bubbly.