Combine the lemon rind, parsley and half the garlic in a small bowl and set aside. Whisk the remaining garlic with olive oil and 2 tablespoons lemon juice in a large bowl, season well with salt and pepper.
Halve the mushrooms and add to the bowl, stir to coat mushrooms in the marinade.
Preheat a barbecue plate over high heat. When hot, add the mushrooms in two batches and cook for 3-4 minutes, tossing occasionally, until tender. Remove to a plate. Trim the asparagus and barbecue 1-2 minutes until bright green and tender.
Arrange salad leaves, mushrooms and ricotta on serving plates. Sprinkle over gremolata. Serve with flatbread.