for the basil oil, put the basil leaves into a food processor with the garlic and seasoning. Process until the basil is finely chopped and with the motor running, slowly trickle in the olive oil and continue to blend until you have a puree.
Blanch the tomatoes, peel them and halve them and remove the seeds; roughly chop up and reserve
Slice the onions into 5mm rounds and spread out on a large baking tray lined with nonstick baking paper, separating them into rings. Sprinkle with the sugar and a generous pinch each of sea salt and freshly ground black pepper. Pour over the balsamic vinegar and olive oil and mix lightly with your hands
Preheat the oven to 200C, fan 180C, gas6; halve the peppers lengthways and remove the cores, seeds and white pith and place skin-side down in a shallow baking tray
Mix the tomato, garlic, basil leaves and anchovy pieces together in a bowl, then divide between the pepper halves. Drizzle with the olive oil and season
Bake the filled peppers for 35 minutes or until they are soft and slightly blackened around the edges, but still holding their shape. At the same time bake the onions, turning them and basting halfway through cooking
Leave the peppers and onions to cool. Arrange the peppers on a plate, scatter the olives and onions over the top and drizzle with the basil oil and serve