Preheat oven to 375°F (190°C). Wipe mushroom caps clean with a damp paper towel; remove stems and finely chop stems (set caps hollow side up on a baking sheet or in a shallow baking dish).

Sauté aromatics and stems

In a skillet over medium heat, warm 1 tablespoon butter and 1 tablespoon olive oil. Add the minced shallot, garlic, and diced celery and sauté 2–3 minutes until softened and fragrant. Add the chopped mushroom stems and cook another 3–4 minutes until moisture evaporates. Stir in chopped parsley and sliced green onions, then remove from heat to cool slightly.

Combine crab-shrimp filling

In a mixing bowl, beat together the softened cream cheese, mayonnaise, lemon juice, Dijon mustard, Worcestershire sauce, hot sauce (if using), salt, pepper, and paprika until smooth. Fold in the sautéed aromatics and stems, then gently fold in the crab meat and chopped shrimp until evenly distributed. Stir in 1/2 cup grated asiago and the breadcrumbs to reach a scoopable consistency — the mixture should hold together but not be overly stiff. Adjust seasoning to taste.

Fill mushroom caps

Using a small spoon, scoop about 1 to 1 1/2 teaspoons of filling (or mound to top) into each mushroom cap. Pack gently so the filling sits neatly in the cavity and slightly mounds on top.

Finishing & Baking

Top and bake

Brush the outside of mushroom caps lightly with the remaining 1 tablespoon melted butter. Sprinkle the tops with the remaining 1/4 cup grated asiago. Place the filled mushrooms on the prepared baking sheet spaced slightly apart. Bake in the preheated oven for 18–22 minutes, until the tops are golden and the mushrooms are tender but not collapsed.

Broil for color (optional)

If you want more browning, switch the oven to broil on high for 1–2 minutes — watch closely to prevent burning.

Finish and serve

Remove from oven, drizzle or brush any leftover melted butter over the tops, garnish with chopped parsley and a squeeze of fresh lemon. Serve warm on a platter with lemon wedges alongside for squeezing.