Preheat the oven to 350°F (175°C). Line a rimmed baking sheet with parchment paper or foil.
In a medium bowl, combine the drained, finely chopped artichoke hearts, softened cream cheese, grated Parmesan, mayonnaise, and thinly sliced scallions; stir until smooth and evenly mixed.
Arrange the mushroom caps, hollow side up, on the prepared baking sheet.
Use a small spoon to fill each cap with the artichoke-cheese mixture, mounding a bit on top of each mushroom.
In a small bowl, stir together the breadcrumbs, Italian seasoning, and olive oil (or melted butter) until the crumbs are evenly moistened.
Divide the breadcrumb mixture among the stuffed mushrooms and press the crumbs gently onto the filling to adhere.
Bake for 12 to 15 minutes, depending on mushroom size, until the filling is heated through and the breadcrumbs are golden brown.
Garnish with additional thinly sliced scallions and serve warm.