1. Place a rack in center of oven and preheat to 425ºF. Line a baking sheet with parchment. In a medium bowl, toss strawberries, orange zest and juice and 1 tsp. brown sugar. In a small bowl, mix 1 cup yogurt with 1 Tbsp. brown sugar. Cover and refrigerate.
2. In a food processor, pulse both flours, remaining 2 Tbsp. brown sugar, baking powder, baking soda and salt. Add butter and pulse until mixture resembles sand. Add remaining 1/2 cup yogurt and pulse just until dough forms. Transfer dough to a lightly floured surface and form into a flat disk about 6 inches by 1/2 inch. Using a floured 2-inch round biscuit cutter, cut out 4 rounds; press scraps together and form 4 more. Arrange rounds about 1 1/2 inches apart on prepared baking sheet. Brush tops with egg; sprinkle with coarse sugar, if desired.
3. Bake until golden brown on top, about 15 minutes. Let biscuits cool on a wire rack for 5 minutes. Halve biscuits horizontally; top with reserved sweetened yogurt, strawberry mixture and biscuit tops. Serve immediately.