Baked anchovy stuffed red mullet with fennel

Name: Baked anchovy-stuffed red mullet with fennel
Ingredients: 1 large or 2 medium fennel bulbs; 1 red onion, sliced into thin wedges; 2 tbsp extra virgin olive oil, plus extra for the stuffing and to drizzle; 1 lemon, juiced, plus wedges to serve; 4 medium whole red mullet, about 350g each, gutted, scaled and washed; crusty bread, to serve; 50g anchovies, drained of oil and finely chopped; 50g fresh white breadcrumbs; 2 garlic cloves, finely grated; 1 plum tomato, finely chopped; 1 tbsp finely chopped flat-leaf parsley leaves