Preheat oven to 350 degrees. Line a rimmed baking sheet with parchment paper or foil for easy cleanup.: Right away you will smell the warm, neutral heat that prepares the oven space, and lining the sheet helps prevent sticking and burning that would ruin the delicate bottoms of the mushrooms . This step ensures an even bake and easier cleanup later. A common oversight is skipping the lining, which can make the bottoms stubbornly stick and tear when you try to remove them. If your oven runs hot, keep an eye on the first batch to gauge timing and adjust placement to the center rack so heat circulates evenly.
In a medium bowl, combine artichoke hearts, cream cheese, Parmesan cheese, mayonnaise, and scallions. Stir until uniformly combined.: As you mix, notice the glossy sheen as the cream cheese and mayonnaise melt into one another and the tiny green flecks of scallions disperse. The scent will shift from sharp artichoke brine to a richer, blended aroma that hints at savory layers. Getting an even texture is important so each mushroom receives the same balance of flavors. A typical mistake is under mixing which leaves uneven pockets of cream cheese; scrape the bowl and fold thoroughly until smooth. If the mixture seems too loose, refrigerate briefly to firm it up before stuffing so it mounds cleanly in the caps.
Arrange mushrooms on baking sheet. Using a small spoon, fill the insides of the caps with the filling and mound additional filling on top of the mushroom.: Placing the mushrooms stem side up creates little bowls that trap the filling, and you should see the creamy mixture gently domed over the rim. The visual cue to look for is a neat mound that holds its shape, not a sagging puddle, and you will feel a slight resistance when you press the filling in. Avoid overstuffing to the point of spilling; that can cause uneven cooking and soggy edges. If your filling is too soft to mound, chill it for a few minutes, then proceed so the tops stay intact during breadcrumbing and baking.
In a small bowl, combine breadcrumbs, Italian seasoning, and olive oil. Using your fingers, divide the breadcrumbs among the stuffed mushrooms, pressing the crumbs into the filling.: Mixing the breadcrumbs with Italian seasoning and olive oil releases herbal aromas and creates a tacky texture that adheres to the filling. When you press the crumbs with your fingers, you should hear a faint crunch and feel the crumbs compact slightly, which is a good sign they will brown nicely. The oil helps the crumbs turn golden rather than remain pale. A troubleshooting tip is to avoid adding too much oil which can make the topping greasy; you want crumbs that cling, not pools of oil. Press gently and evenly so each mushroom ends with a consistent crust that will crisp up in the oven.
Bake for 12 to 15 minutes, depending on the size of the mushrooms, until the breadcrumbs are golden brown and the filling is heated through. Garnish with thinly-sliced scallions.: During baking you will notice the kitchen fill with roasted mushroom aroma and a warm, toasty scent from the breadcrumbs as they brown. Visual cues are essential here the crumbs should take on an even golden tone while the filling becomes slightly puffed and steaming at the edges. A common mistake is leaving them in too long which can dry the filling and make the mushroom rubbery. To test doneness, look for bubbling around the edges and a light jiggle in the center. Once out, the thinly sliced scallions sprinkled on top will add a bright, fresh contrast both in flavor and appearance. Let them cool briefly so the filling sets slightly before serving.
