Finely slice the onion and garlic.
Heat the oil in a frying pan and gently sauté the onion and garlic over a low heat for about 6-8 minutes.
Meanwhile, chop the liver and shitake into bite-sized pieces.
When the onion has softened, add the liver and mushroom pieces. Turn up the heat and stir-fry for a minute, allowing the liver to change colour.
Add the soy sauce, rice vinegar, some lime juice and the beans. Put a lid on and turn the heat down.
Sautee for 5-10 minutes. Make sure the liver is not overcooked (or it will taste rubbery).
When the liver is cooked through, add a drop of sesame oil and a handful of chopped parsley or coriander. Season with ground peppercorn and chilli flakes (if liked), then combine.
Serve immediately.