Rhubarb Berry Slab Pie

Name: Rhubarb Berry Slab Pie
Ingredients: 2 cups all-purpose flour (280 g); 1 cup white whole wheat flour (150 g); 1 1/2 cups quick cook or baby rolled oats (150 g); 1 teaspoon kosher salt; 1 1/2 cups unsalted butter (340 g or 3 sticks); 3/4 cup cold water (plus an additional 1/4 cup if necessary); 3 cups halved strawberries (455 g or 1 lb); 2 cups blueberries (300 g or 10 1/2 oz); 3/4 cup granulated sugar (divided, 150 g); 1/4 cup cornstarch (35 g); Zest of 1 lemon; 1/4 teaspoon kosher salt; 1/4 teaspoon fresh ground pepper; 5 cups 1/2-inch chopped rhubarb (625 g or 1 lb 6 oz); 1 teaspoon balsamic vinegar; 1 large egg; 1 tablespoon cold water; 2 tablespoon Turbinado sugar (or white sugar)