Clean the onions and cook them, whole, in boiling water with 1 spoonful of Balsamico Bianco for 10 minutes. Then strain and leave them to cool slightly. Wash and dry the cherry tomatoes, cut them into small pieces and set them aside. Mix the grated pecorino with the breadcrumbs in a bowl, and then sprinkle a couple of spoonfuls of this mixture in the bottom of an oven dish greased with 2 spoonfuls of oil. Cut the onions into wedges and arrange them in the oven dish. Scatter the pieces of cherry tomato, capers and olives over them, and season with salt and pepper. Sprinkle with the remaining breadcrumb and pecorino mixture, add a drizzle of olive oil and cook in a preheated oven, at 180 °C, for 20 minutes. Before serving, garnish with fresh parsley (just the leaves, washed, patted dry and chopped).