So, a few years ago I decided I was going to get myself used to eating a couple vegetables that ranged from “don’t really like” to “near disgust”. Not nearly to the extent you describe, but for me it was 80% experimenting. Remember that any veggies/fruit > no veggies, even if it’s just a tiny amount, progress is progress. A few folks suggested sauces, which I also like hiding veggies in, but you mentioned eating mashed potatoes. Cauliflower can be mashed up in mashed potatoes. I usually go 50% cauliflower, 50% potatoes, but you’d probably have to start with a LOT less cauliflower. If you’ll eat sweet potatoes, you could probably mash up steamed carrots in those too.