Heat oven to 350°F. Grease a 9×5-inch loaf pan and line with a parchment sling.
Make streusel: Stir flour, brown sugar, granulated sugar, and cinnamon. Cut in cold butter until clumpy. Chill.
Whisk dry batter ingredients: flour, baking powder, baking soda, salt, cinnamon, and nutmeg in a large bowl.
Whisk wet batter ingredients: granulated sugar, brown sugar, eggs, oil, milk, and vanilla until smooth.
Combine wet into dry. Stir gently just until no dry streaks remain; do not overmix.
Fold in the diced apples until evenly distributed through the batter.
Spread half the batter in the pan. Sprinkle on half the streusel. Add remaining batter, then the rest of the streusel.
Bake 50–58 minutes, until a toothpick in the center comes out clean. Tent with foil if browning quickly.
Cool in the pan 15 minutes, then lift out to a rack and cool until just warm.
Whisk glaze ingredients to a drizzle. Adjust milk as needed. Drizzle over cooled bread and slice.