A filled treat is a type of food that has been filled with a variety of ingredients. The two crossword solutions for this term are pierogi and Oreo. Pierogi is a type of dumpling that is filled with savory ingredients such as potatoes, cheese, and onions. It is a traditional dish in Eastern European countries. Oreo is a type of cookie that is filled with a sweet cream filling. It is one of the most popular cookies in the United States.