Leave it to simmer gently for 10 minutes then add the basil and check the seasoning adding a little salt and pepper if necessary (but note the two cheeses will add quite a bit of salt to the finished dish)
Meanwhile put a griddle pan or non stick frying pan on a high heat and then slice the aubergine into approximately 1cm discs (should make about 10) and coat them in the olive oil (note - I never salt aubergines, I think it's a waste of time)
Cook the sliced aubergine on the griddle or frying pan in batches for about 5 minutes, turning halfway through when they are nicely browned
Use a small oven proof dish and put a layer of the tomato sauce on the bottom followed by a layer of cooked aubergine, some mozzarella and a sprinkle of parmesan then repeat once or twice, depending on the size of your dish but finish with a layer of mozzarella and a good sprinkling of parmesan.
Put it in the oven for 25 - 30 minutes until it is golden brown and bubbling
Recipe by Cook Low FODMAP at https://cooklowfodmap.com/low-fodmap-baked-aubergine-and-mozzarella/