Cook barley in a pot of boiling salted water until tender. Drain; spread out on a clean tray and allow to cool.
Heat a drizzle of olive oil in a large frying pan over medium-high. Cook mushrooms until golden brown all over. Season mushrooms with salt and pepper. Add garlic, shallots, butter and thyme and cook until just tender and fragrant.
In a large bowl; toss cooled barley with cooked mushroom mixture. Fold in coriander, parsley, lemon juice and taste for seasoning.Arrange endive leaves on a large platter or in individual bowls. Spoon over the herby mushroom and barley mix and serve.