Heat the oil in a large skillet over medium-high heat and saute the mushrooms until brown and almost all the liquid has evaporated.

Add the chopped spinach and white wine and cook until wilted and almost all the liquid has evaporated. Season with salt and pepper and put this mixture into a medium-sized bowl.

Using the same skillet, melt the butter and saute the onion and garlic until translucent and fragrant. Pour the marinara sauce into the skillet and add the Italian seasoning. Simmer the sauce for about 8 minutes.

While the sauce is simmering, boil the pasta shells until almost cooked, but still firm (al dente). Drain and reserve. Remember not to overcook the shells or they will break when you stuff them. They will continue cooking in the sauce.

To the bowl with the mushroom/spinach mixture, add the ricotta cheese, 1 cup of parmesan cheese, and the chopped oregano. Season with more salt and pepper if needed. Mix until well combined.

Stuff each shell with about 1 ½ - 2 tablespoons of the filling.

Place the stuffed shells in a circular pattern on top of the sauce and into the skillet, sprinkle with the remaining ¼ shredded parmesan and place the lid on. Simmer the shells in the sauce for about 5-6 minutes or until the cheese has melted. You can also place the skillet into a preheated 350 F oven and bake them until the sauce is bubbly and the cheese has melted.