Preheat oven to 400 degrees. Heat a cast iron skillet on high heat until smoking.Sprinkle beef on both sides with salt. Cut beef into 3/4 inch cubes. Add oil to pan. Brown the meat no more than 30 seconds. Remove meat onto a plate and set aside. Lower heat to medium and add mushrooms to pan and saute until done. Salt and Pepper to taste and remove to plate and set aside. Saute Spinach in pan and set aside. Add onion to pan and saute for 2 minutes. add marsala wine and cook until the wine is reduce by half. Add the preserves and transfer contents to a food processor and puree. Set the sauce aside.
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.