Lay the mushrooms on a large baking tray and sprinkle with the onions, garlic and thyme.
Top the mushrooms with the slices of Taleggio. Toss together the breadcrumbs and the parsley and sprinkle over the mushrooms.
Bake for 15 to 20 minutes in the preheated oven until breadcrumbs are brown and the mushrooms are cooked through.
Meanwhile, dress the rocket with the lemon juice and some olive oil. Serve the mushrooms with the dressed rocket. P.S. They’re great on toasted ciabatta too!