Heat oven to 350. Grease and flour 12-cup bundt cake pan. Prepare Streusel Filling. Mix remaining ingredients except apples and powdered sugar; beat vigorously 1 minute. Spread one third of the batter (about 1- quarter cups) in pan and sprinkle with half of the Streusel Filling (about quarter cup) and half of the apples; repeat. Spread with remaining batter. Bake until wooden pick inserted near center comes out clean, 45-50 minutes; cool 10 minutes. Invert on heatproof serving plate; remove pan. Sprinkle cake with powdered sugar. STREUSEL FILLING: Mix all ingredients until crumbly. GLAZE: Heat margarine or butter in saucepan until melted. Stir in powdered sugar and vanilla. Stir in 1-2 tb milk, 1 ts at a time, until smooth and of desired consistency. ----