Preheat oven to 350°F. Place melted butter in a 9- x 9-inch baking dish.
Gently stir sliced strawberries, lemon zest, lemon juice, and 1/4 cup of the sugar in a large bowl until totally combined. Let strawberry mixture stand, stirring occasionally, until juicy, about 15 minutes.
Whisk together flour, baking powder, salt, baking soda, and remaining sugar in a medium bowl until combined.
Whisk together buttermilk and vanilla in a glass measuring cup. Add buttermilk mixture into flour mixture, and continue to stir until the batter is smooth.
Pour the dough mixture evenly over melted butter. (Do not stir.) Using a slotted spoon, scatter strawberry mixture evenly over batter.
Drizzle 3 tablespoons of accumulated juice from bottom of bowl over strawberries. Discard any remaining juice.
Bake in preheated oven until batter is puffed and slightly golden in the center and dark golden brown around edges, 30-35 minutes. Cool on a wire rack at least 15 minutes. Serve warm with ice cream.