Lay green beans in steamer of choice; cover. Steam over high heat until beans are crisp-tender, about 15 minutes.
While beans are steaming, heat oil over high heat in a large nonstick skillet. Add garlic, cook, stirring until garlic is cooked through but now brown.
Add mushrooms cook, stirring and flipping, until mushrooms exude moisture and begin to brown, about 7 minutes. Add seasonings and wine or sherry, stir. Continue cooking until alcohol evaporates, 1 to 2 minutes. Cover with lid; set aside.
Transfer steamed beans to serving plate. Pour mushrooms over top. Serve immediately.