Preheat oven to 375°F. Line a baking sheet with parchment paper. Pulse flour, oats, almonds, 1/3 cup sugar, baking powder, and salt in a food processor until finely ground. Add butter; pulse until only pea-size pieces remain. Add 1/2 cup cream and 1 teaspoon vanilla; pulse until large moist clumps form. Transfer to a work surface. Knead until dough comes together, about 4 turns. Pat into a 4x6" rectangle. Halve lengthwise, then crosswise into thirds. Arrange on prepared baking sheet. Brush with cream; sprinkle with 1/2 tablespoon sugar. Bake, rotating sheet halfway through cooking, until golden brown around edges and a tester inserted into center comes out clean, about 20 minutes. Set biscuits on a wire rack; let cool. DO AHEAD: Biscuits can be made 8 hours ahead. Store cooled biscuits airtight at room temperature. Meanwhile, combine strawberries, 1 tablespoon sugar, and Grand Marnier, if using, in a large bowl. Toss to coat. Let strawberries sit, tossing often, until juices release. Whisk 1/2 cup cream, 1/2 tablespoon sugar, and 1/2 teaspoon vanilla in a small bowl until peaks form. Cut warm or room-temperature biscuits in half; place bottom halves on plates. Divide whipped cream and strawberries over. Top with remaining biscuit halves.