Throw the peppers and garlic into the onion pan, give everything a good stir and cook, covered, over a low heat for 20 mins or so until the vegetables are really soft and sweet. Stir regularly so that they don’t catch on the bottom of the pan. Add the tomatoes, a pinch of sugar and cook, uncovered, for 5 mins more. Season and stir in the vinegar and the basil. Allow to cool to room temperature, stir through the basil and taste to check the flavours again. You may want to add a dash more vinegar, or a pinch more sugar, depending on how sweet your vegetables are. Spoon onto the baguette slices and serve.