Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with butter or non-stick spray.
In a large bowl, combine the sliced peaches, 1/2 cup of the sugar, cinnamon, and lemon juice. Toss gently to coat the peaches evenly. Pour the peach mixture into the prepared baking dish.
In another bowl, whisk together the flour, remaining 1/2 cup of sugar, baking powder, and salt. Add the milk, melted butter, and vanilla extract. Stir until just combined; do not overmix.
Pour the batter over the peaches in the baking dish, spreading it evenly. Do not stir; the batter will rise while baking.
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.
Remove from the oven and let cool for about 10 minutes before serving.