Preheat oven to 375 F. Combine berries, sugar, flour, lemon juice, lemon zest, and salt in a large bowl, then toss gently to combine.
Roll out 1 disk of dough on a lightly floured surface, then carefully transfer to 15" x 10" x 1" sheet pan. The dough should be about 2" longer than your pan on either side -- so about 17" x 12". Use your hands go lightly press the dough into the bottom and up the sides, allowing any excess dough to hang over the edge. If the dough breaks to tears, simply use your hands to press it back together -- this dough is very forgiving!
Pour mixed berries into prepared pie dough and spread into an even layer.
Roll out the remaining pie dough on a lightly floured surface. At this point you can transfer the entire dough over to the sheet pan for a fully covered pie, or you can cut the dough into long strips and create a lattice pattern.
To make a lattice top: place half the strips diagonally across the sheet pan. Weave the remaining strips to form a lattice pattern. Again, if the dough breaks, simply press back together.
Trim edges so that dough is even with the sides of the pan, tucking the bottom dough over the top dough as needed, then use your fingers or a fork to crimp or pattern dough along the sides.
Brush the top of the pie with beaten egg, then sprinkle with turbinado sugar. Bake for 40-45 minutes, or until crust is a deep golden brown and berries are bubbling. Let cool about 5 minutes before slicing. Serve with ice cream or whipped cream.