Heat the oil in a small frying pan and add the garlic. Stir-fry for about 1 minute, then add the shiitake mushrooms and soy sauce. Cover the pan and cook gently for about 8 minutes, stirring occasionally. Add a little water if the mushrooms become too dry or start to stick.
Add the spring onions and cook for a further 3 minutes. The mushrooms should be tender and there should be a little sauce in the pan. Add a splash of water if necessary.
Meanwhile, put the cooked brown rice into a mixing bowl.
Peel the eggs and cut each into four wedges.
Peel the avocado and cut it into slices. Drizzle with a little lemon juice to prevent it from browning.
Add the shiitake mushrooms and their sauce to the rice, together with the chopped coriander. Mix well, then season with the remaining lemon juice, salt and pepper to taste.
Divide the rice salad between two plates and arrange the egg and avocado slices on top.
Scatter with sesame seeds or ground black cumin seeds and serve.