2.Combine oyster, shiitake, swiss brown and flat mushrooms, tomato, onion, garlic and oil in large baking dish; roast, uncovered, in slow oven about 30 minutes or until mushrooms are tender.
3.Meanwhile, soak porcini in the boiling water in small jug for 15 minutes. Drain over small bowl; reserve liquid. Chop porcini finely.
4.Combine reserved liquid, milk and the cold water in medium saucepan; bring to a boil. Gradually add polenta to pan, stirring. Reduce heat; cook, stirring, about 5 minutes or until polenta thickens slightly. Stir in porcini, butter and cheese.
5.Stir herbs into mushroom mixture. Divide polenta among serving plates; top with mushroom mixture.