In a bowl, combine sliced peaches, blueberries, and lemon zest; toss to combine.
Arrange fruit mixture on the bottom of pie crust.
In your mixer's bowl, combine sweetened condensed milk, eggs, lemon juice, vanilla, and butter; beat until smooth and combined, about 30 seconds.
Pour custard over fruit-mixture; set aside.
In a small mixing bowl, combine flour, light brown sugar, and chopped pecans; using a pastry blender, cut in butter until mixture resembles coarse crumbs.
Sprinkle Streusel Topping on top of custard.
Bake pie for 55 to 60 minutes, or until toothpick inserted in the center comes out clean.
Remove from oven and cool on wire rack, over night.
Cut and Serve.