Preheat your oven to 350°F (175°C) and lightly grease a baking dish.
In a large mixing bowl, toss sliced peaches with granulated sugar, ground cardamom, and lemon juice until evenly coated. The peaches should look juicy and fragrant.
Pour the peach mixture into the prepared baking dish, spreading it out into an even layer.
In a separate bowl, combine oats, flour, and brown sugar, mixing well.
Add the cold, cubed butter to the dry ingredients. Using your fingertips or a pastry cutter, work the butter into the mixture until it resembles coarse crumbs with some pea-sized bits.
Sprinkle the crumbly topping evenly over the peaches, covering them completely for a uniform crust.
Bake in the preheated oven for about 40 minutes, until the topping is golden brown and the peach filling is bubbling around the edges.
Remove from the oven and let it cool slightly—this helps the juices thicken and makes serving easier.
Serve warm, optionally topped with a scoop of vanilla ice cream or a dollop of whipped cream for added indulgence.
