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 gently to coat the peaches and set aside to marinate for about 15 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. Do not overmix; a few lumps are okay.
Pour the batter into a greased 9x13-inch baking dish.
Spoon the marinated peaches and their juices 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 into the batter comes out clean.
Allow to cool for at least 10 minutes before serving.