Heat olive oil or butter in a frying pan over medium heat. Add the sliced mushrooms and cook for 6 to 8 minutes, stirring occasionally, until the mushrooms release their moisture and become golden and slightly caramelised. Season with salt, pepper, thyme and garlic powder if using.
Butter one side of each slice of bread.
Lay slices of bread butter-side down. Spoon the cooked mushrooms evenly across the slices, then sprinkle grated cheese over the top.
Place the remaining bread slices on top, butter-side up.
Heat on a pan or sandwich press. Cook each toastie for 3 to 5 minutes, or until the bread is golden and crispy and the cheese has melted.
Remove, cut in half and serve hot with BBQ sauce for dipping.
6 servings