Lay out 1 fillo sheet and brush with butter. Continue adding layers until you have 5 sheets. Cut into 4 strips. Put a teaspoon of spinach on one end of the fillo dough. Top with 1 cube of beef and 1 mushroom. Roll up, tucking ends in so it looks like a miniature egg roll. Brush the top with butter and bake on a prepared cookie sheet for 12 minutes. Arrange on a platter, top with marsala sauce and garnish with arugula and avocado.