Adjust oven rack to lowest position and heat oven to 450 degrees. dissolve 5 teaspoons salt in 2 quarts room-temperature water in large container. Add cremini mushrooms and shiitake mushrooms to brine, cover with plate or bowl to submerge, and let stand for 10 minutes.
Drain mushrooms in colander and pat dry with paper towels. spread mushrooms evenly on rimmed baking sheet, drizzle with oil, and toss to coat. Roast until liquid from mushrooms has completely evaporated, 35 to 45 minutes.
Remove sheet from oven (be careful of escaping steam when opening oven) and, using thin metal spatula, carefully stir mushrooms. Return to oven and continue to roast until mushrooms are deeply browned, 5 to 10 minutes longer.
Combine melted butter and lemon juice in large bowl. Add mushrooms and toss to coat. Add parmesan, pine nuts, and parsley and toss. Season with salt and pepper to taste; serve immediately.