Cut 4 12-inch squares foil. Spoon 1/3 cup beans and 1/2 cup mushrooms in center of each foil square.Combine tomatoes, feta, olives, rosemary, and garlic oil in bowl. Divide mixture among foil packets, and season with salt and pepper. Bring up sides of foil to meet over contents, fold edges together, and then fold a few times over contents to form a packet. Fold edges over to seal. Place packets in bottom portion of bamboo steamer. Arrange Swiss chard leaves in steamer’s top basket. Top with polenta rounds.Fill large skillet or wok with 2 inches water. Cover, and bring to a boil over high heat. Place steamer in skillet, and steam 10 minutes.To serve: Place 2 polenta rounds and some Swiss chard leaves on each plate. Open packets, and slide contents over polenta. Sprinkle with parsley.