Preheat oven to 375°F (190°C). Lightly oil a baking sheet.

Sauté shallot and garlic in 2 tbsp olive oil until softened, then add sausage and cook through. Break up pieces and drain excess fat.

Stir in panko, Parmesan, parsley, and seasonings; remove from heat and let cool.

Fill mushroom caps with sausage mixture, place on sheet, brush tops lightly with oil.

Cover tightly and refrigerate overnight. Next day bake 18–22 minutes until mushrooms are tender and filling is golden.