Final answer:
The garlic peppercorn dressing does contain mushrooms as indicated by the inclusion of a can of mushrooms and liquid in the recipe.
Step-by-step explanation:
Yes, there are mushrooms in the garlic peppercorn dressing. According to the provided ingredients list, one of the components is '1 (8 ounce) can mushrooms and liquid,' which indicates that mushrooms are indeed part of the recipe. Furthermore, the mention of 'Oyster mushroom (Pleurotus ostreatus) mycelium in petri dish on coffee grounds' in relation to a Creative Commons license implies that mushrooms, especially the oyster variety, are a topic of interest in this context but does not affect the presence of mushrooms in the dressing recipe itself.