Preheat oven to 350 degrees. Combine sugar and tapioca, add apricots and lemon juice. Toss to coat. Let stand for 15-20 minutes. Sprinkle 2 teaspoons of flour into bottom of pie crust to keep it from being soggy. Spread evenly over bottom of crust with your fingers. Pour filling into crust; set aside.
Prepare topping: Combine flour, sugar and nuts. Stir in melted butter. Sprinkle topping over filling. Cover edges of pie loosely with strips of foil (prevents burning). Bake for 15 minutes, remove foil. Continue baking for another 25-30 minutes (until golden brown, bubbly filling). Cool on wire rack. Serve warm. Store leftovers in the refrigerator.