Preheat oven to 400°F/204°C.
Clean the mushrooms, including the stem by wiping them with a paper towel.
Remove the stems from the mushrooms and dice them into small pieces and set aside.
In a large skillet, over medium heat, melt the unsalted butter and add the diced mushroom stems and saute about 4 minutes to soften the mushrooms.
Add in the garlic and spinach to wilt the spinach and blend in the garlic flavor, about 1 more minute.
To the pan, stir in the diced artichokes, cream cheese, shredded mozzarella, Panko breadcrumbs, salt, and black pepper. Taste for seasoning.
Taste the stuffing mixture, if needed, adjust seasoning. Set aside.
In a small bowl, add the olive oil, use a pastry brush to dip into the olive oil and coat the mushroom caps lightly with the olive oil. Then place the mushrooms on the baking tray.
Use a teaspoon to fill each mushroom cap with the filing. Press filling inside the cavity of the mushroom. Usually, about 2 teaspoons of the filling will fill the mushroom and place the stuffed mushroom on the baking tray.
When all mushrooms are filled, place the baking tray in the preheated oven i the oven for about 10-12 minutes until mushrooms are golden brown and cheese is melted.
Serve and enjoy.