To prepare the stuffed portabello burger with vegetarian herb aioli cheese recipe, you will first need to prepare your ingredients. You will need: 2 tbsp. olive oil, 2 tablespoons vegetable shortening, 1 tablespoon kosher salt, 1/2 teaspoon ground black pepper, and 1 teaspoon thyme sprigs or chives. To make the filling: Place the cut side down on the baking sheet and cover with aluminum foil. Bake in the preheated oven for 20 minutes. Remove the foil and bake for an additional 10 to 15 minutes or until the cheese is melted and bubbly.