Making good use of your freezer can really help - make double quantities of pretty much everything that can freeze and save the extra ready for future meals. I use extra large ice cube trays to make 5cm cubes which stack well and are easy to portion out. A big batch of tomato sauce will do pasta sauces, pizza and you can add extra veg or lentils to make other dishes too. Chilli and bolognese are great freezer standbys too. I keep jars of minced garlic and ginger in the fridge and chopped onions and stir fry veg in the freezer, which all speed up meal prep. Frozen soft fruit is cheap, low waste and great for desserts or stirring into yoghurts or cereal.
A well stocked spice and condiment cupboard helps too - really makes the difference to being able to create tasty food. It may not have the addictive hit of UPF but it can still taste great.
A bread machine will really help, not just for bread (which can be a substantial source of UPF in the diet and tastes so much better home made), but also for doughs for pizza bases, naan and so on.
If you use a lot of UPF sauces etc, cood cook books are worth investing in to help you work out quick ways to make UPF-free alternatives - I love Nigel Slater's Real Fast Food and Rukmini Iyer's Roasting Tin series.
And at the end of the day, we're generally talking about reducing UPF not eliminating entirely - if there's something that really works for your family (quorn is my weakness as it's so convenient!) then keep it as a small part of your diet and don't worry, particularly about items added in really small quantities.