Saute mushrooms and garlic in butter. Add rest of ingredients and set aside.  Using 3-4 sheets of phyllo, cut lengthwise into 4 long strips.  Cover with damp cloth. Take two strips and lay them out on top of the other. Lightly brush with oil. Place about one tablespoon of filling at the bottom of the strip. Fold one corner over the filling, alternating from left to right until you reach midway. Brush the pastry again with a little butter or oil. Continue folding to the end. Place the triangle seam side down on a greased baking sheet.  Brush top with more butter or oil.  Bake at 350 degrees until golden brown (approximately 20 minutes).