Preheat your oven to 350°F (175°C).
In a large bowl, combine the sliced peaches, 1/2 cup of sugar, cinnamon, and lemon juice. Toss to coat and set aside to marinate for about 10 minutes.
In another bowl, whisk together the flour, baking powder, salt, and remaining 1/2 cup of sugar.
Stir in the milk, melted butter, and vanilla extract until just combined. The batter will be slightly lumpy, which is okay.
Pour the batter into a greased 9x13-inch baking dish.
Spoon the marinated peaches evenly over the batter. Do not stir; the batter will rise around the peaches as it bakes.
Bake in the preheated oven for 40-45 minutes or until the top is golden brown and a toothpick inserted in the center comes out clean.
Allow to cool for at least 15 minutes before serving.