These easy Marinated Mushrooms are bursting with savory, tangy flavor from a blend of shiitake mushroom oil, rice wine vinegar, garlic, and Italian seasoning. Baby portabellas are simmered in a fragrant marinade, then chilled overnight to soak up all that umami goodness. Perfect as an appetizer, salad topper, or charcuterie board addition, these mushrooms are make-ahead friendly and full of bold, earthy flavor that only gets better with time.