Finely dice the artichoke hearts. Make sure the pieces are small enough to fit inside the mushrooms.
Heat oil in a pan over medium-low heat.
Add the spinach, garlic, and salt. Cover, and allow spinach to wilt. Remove the lid, and press down on the spinach to release extra liquid. Scoop the spinach out of the pan and into a mixing bowl. Discard extra liquid.
Add the artichokes, cream cheese, and yogurt to the mixing bowl. Stir until incorporated.
Use a spoon to scoop the mixture into the mushrooms, filling the space where the stem used to be. Tip: Filling amount is approximate, and the amount you need will depend on the size of the mushrooms you use. Extra filling can be warmed and used as chip dip or sandwich spread.
Place mushrooms on a baking sheet, and top with freshly grated Parmesan.
Roast 20-25 minutes, or until the cheese is golden and the mushrooms are tender. Serve warm.
Prep Mushrooms Ahead: Up to 1 day ahead, stuff the mushrooms, set on a baking sheet, and tent with foil. Wait to roast until just before serving.Make Mushrooms Ahead: Up to 1 day ahead, fully cook the mushrooms. Leave them on the baking sheet, and cover with foil. Put them in the refrigerator. When you’re ready to serve them, broil the mushrooms 2-3 minutes, or until hot.
Serving size + nutrition information estimates 1 mushroom per person.