Take a 2- or 3-qt bake dish and add the marinara in a layer.
To prepare the mushrooms, gently brush the dirt off each using a damp paper towel. Break off the stems, chop the stems, and set aside. Take the mushroom caps and brush tops and bottoms very lightly with olive oil. Place them, bottom-sides up, into the bake dish on the marinara.
In a mixing bowl, use a fork to combine the chopped mushrooms stems and remaining ingredients. Mound the stuffing into the mushrooms caps. Bake for 20 minutes until stuffing is heated through and lightly browned on top.