We are all conditioned to think you start every single savoury dish by frying something in oil, so it’s a revelation when you realise you can sautee in water.
I like to make my soup base with diced onion, carrot and celery. I heat up the pan then add a quarter a cup of water and when it is hot I add the diced vegetables and start to stir. As the water evaporates and the vegetables soften I just add extra water a tablespoon at a time. I like them to sizzle and I stir them frequently so they don’t stick. If you were making a stew however, you could let the onions brown a little and then deglaze with wine or stock.
Taking oil out of your diet little by little is a positively healthy step in your plant-based journey.