Maduros are a very popular ingredient in Cuba. They are plantains that are ripe and sweet, as compared to green plantains. The riper and blacker the plantains are, the sweeter they will be when cooked.
For the filling: Place oil in a Dutch oven at least 4 inches deep and heat to 375 degrees F. Fry the plantains until golden brown, about 2 to 4 minutes. Remove, drain on paper towels, then chop into rough dice.
In a medium skillet over medium heat, add chorizo. Stir to break up the meat and brown evenly, about 4 to 5 minutes. Remove from heat, add plantains and set aside.
For the mushrooms: Line a rimmed baking sheet with parchment paper. Place mushrooms cap-side up on the baking sheet. Drizzle with olive oil and sprinkle with salt and pepper. Roast in the oven 10 to 12 minutes.
Remove mushrooms from oven and fill cavities with chorizo mixture. Sprinkle mozzarella on top followed by Cotija. Place back in the oven until cheese has melted, 10 to 12 minutes. Serve.