Okay, first off the tomato sauce. Most people would probably use a ready made, but for the sake of it, i’ll write the recipe out in full.
for the tomato sauce, chop up an onion, put it in a pan with olive oil until they brown, then add a clove of garlic (crushed/finely chopped). Once these are soft and translucent, add a can of diced tomatoes. Season with a teaspoon of sugar, and salt and pepper, and let it simmer for about 30 minutes (at which point you turn down the heat a bit).
the tomato sauce you can make well ahead of time, and use it for multiple dishes.
now, heat up a pan with a good dose of olive oil. Chop up the mushrooms, aubergine, and courgette and add to the pan. Leave them in until soft, then add to the tomato sauce and let it simmer for a little while longer (maybe 10 minutes).
if you want to, it tastes great with couscous, and a little bit of feta cheese crumbled on top. Or, simply eating it with a piece of meat!