Preheat oven to 425°F.
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 with the cauliflower, one tablespoon of the melted butter, 1 ½ tablespoon 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.
Roast the cauliflower until golden brown on top, about 10 minutes. Sprinkle with parsley and serve warm.
