Preheat oven to 425 degrees. Line a baking sheet with parchment paper; set aside.
In a large bowl, whisk the flour, baking powder, and salt together. Use a pastry blender to cut in the butter until the mixture resembles coarse meal. Stir in the scallion, then add the buttermilk and stir until the dough just comes together.
On a floured surface, pat or roll dough to 3/4-to-1-inch thickness and cut into 3-inch rounds, reforming scraps as needed. You will get about six to eight biscuits. Arrange 2 inches apart on the prepared sheet.
Bake about 15 minutes, until golden brown.
Make the tomato salad:
In a bowl, whisk together everything except the tomatoes. Halve or quarter the tomatoes, then add them to the bowl with the dressing and toss to combine.
Make the whipped goat cheese:
In a separate bowl, use an electric mixer to whip the cream until peaks form. Add the goat cheese and beat until the mixture is light and fluffy.
Assemble the shortcakes:
Split each warm biscuit in half. Generously spoon each half with the tomato salad and dressing. Dollop with whipped goat cheese and sprinkle with scallions. Serve immediately.