Preheat oven to 500°F.
Put coriander seeds, fennel seeds, peppercorns, and star anise in a small saucepan over low heat. When they are warm and fragrant, remove from pan and crush until powdery, using a mortar and pestle or coffee grinder.
Cut mushrooms into halves or thick slices of roughly the same size, toss with 1/4 cup oil and salt, and divide between two sheet pans. Roast for 10–15 minutes, or until mushrooms are nicely browned.
While mushrooms are roasting, transfer spices to a large mixing bowl with garlic, cilantro, dill, celery rib and any leaves, sugar, remaining oil, and sherry vinegar.
When mushrooms are nicely browned, remove them from the oven and add to the bowl while still hot. Pour a splash of water into each hot pan, swirl it around, and pour over the mushrooms, scraping any browned bits off the pan. Mix well, and taste. Adjust for seasoning. Allow to sit overnight in the refrigerator before serving. Serve with bread and goat cheese.