Gather and prep all ingredients. Preheat the oven to 375°F. Lightly butter a shallow 2-quart casserole dish.

Sauté the mushrooms. Melt 2 Tbsp butter in a large skillet over medium heat. Add 8 ounces thickly sliced mushrooms and the white portions of the sliced green onions, reserving the green parts. Season with ¼ tsp salt, ¼ tsp white pepper and ¼ tsp red pepper flakes. Sauté until the mushrooms are tender and have given up most of their liquid. Remove from the heat.

To make the cream sauce, melt 3 Tbsp butter in a saucepan over medium heat. Whisk in 3 Tbsp all-purpose flour and cook for about 2 minutes, stirring constantly, without letting the mixture brown. Gradually whisk in 1½ cups half-and-half. Continue cooking and stirring until the sauce is smooth and quite thick. Season with ½ tsp salt, ½ tsp white pepper and ¼ tsp red pepper flakes. Remove from the heat and stir in 2 Tbsp chopped fresh parsley, ¼ cup grated Parmesan, 1 tsp finely grated lemon zest and 2 Tbsp fresh lemon juice. Taste and adjust the seasoning if needed.

Assemble the casserole. Arrange 2 (14-ounce) cans quartered artichoke hearts, drained and dried very well, in the bottom of the prepared casserole. Scatter about half of the reserved green onion tops over the artichokes, setting about 2 Tbsp aside for the garnish. Add the sautéed mushroom mixture, spreading it evenly across the artichokes. Gently distribute 1 pound lump crabmeat over the mushrooms, taking care to preserve the lumps. Spread the cream sauce evenly over the crab, mushrooms and artichokes, gently distributing it so the sauce nestles into the layers.

For the topping, combine ½ cup panko breadcrumbs, ¼ cup freshly grated Parmesan cheese, ⅛ tsp red pepper flakes and 2 Tbsp finely chopped fresh parsley. Add 2 Tbsp melted butter and toss until the crumbs are evenly moistened. Sprinkle evenly over the casserole.

Bake at 375°F for 20–25 minutes, until hot and bubbling around the edges and lightly golden on top. If more browning is desired, broil briefly at the end, watching carefully. Garnish with 1 Tbsp chopped fresh parsley and the remaining sliced green onion tops, if desired. Let rest for a minute or two and serve hot with crusty bread and butter, and some kind of a salad on the side.