Preheat oven to 425F.
Bring a large saucepan of water to a boil over high heat. Add the cauliflower and lemon wedge. Lower the heat and simmer until tender, about 10 minutes.
Drain, blot dry and transfer to a large bowl. Toss the lemon.
Stir in 1 tablespoon of the melted butter, 1 ½ tablespoons of the breadcrumbs, and the eggs, capers, garlic, oil, salt and pepper. Transfer into a large, oval gratin baking dish.
In a small bowl, stir together the remaining breadcrumbs and remaining 1 tablespoon of butter, and sprinkle over the top.
Bake until golden brown on top, about 10 minutes. Sprinkle with parsley and serve warm.