For comparison & for purposes of research you understand I felt compelled to try a “Slug Burger” at the Slug & Lettuce by the river in Richmond.
A moist organic burger, nicely presented with the onion ring perched on the mushroom stalk, tasty bbq sauce and a whole basket of chips.
From the Menu “SLUG ULTIMATE BEEF BURGER, With mushroom, Cheddar, bacon, beer-battered onion rings and a BBQ sauce. All of our beef burgers are made with 100% British organic beef and served with seasonal salad leaves, gherkin, tomato, red onion and fries. Our beef burgers are available in two sizes — single £10.45 or double £12.45.” Pic below shows the single.