Cheap, easy way to scarf down some fiber?

Hello all.

I hate veggies. Well, most of them. I can tolerate broccoli, carrots, spinach, and even then only with enough seasoning. I wasn't raised on abundant veggie sides with my meals, and I'm still trying to unlearn it. Uphill battle.

But anyway. I've noticed I consume barely any fiber in a day. I have my coffee, my (usually frozen) lunch, and then dinner. I'm 20, and with things like colon cancer on the rise, let's just say I've been scared straight. I'm trying to get better at this little by little.

My first step to this has been the consumption of chia seeds. I add a dollop of them, soaked, mixed into yogurt with berries in the morning lately. Can barely taste it so it works out for me.

Even then, it's only yielding about 10g of fiber if I stick to that. I'd still need to add another 10-15g to have the amount of fiber I need. I looked up lists of high fiber foods, and of course, all veggies, most of them being ones I don't like. I already work most of the day and coming home to cook drains me. Ideally it would be something I can prep for the week, or atleast for a few days.

In short, I really need another way to basically scarf down 10-15g of fiber in a day as quickly and as painlessly as possible. I could cop out and do a fiber supplement or maybe one of those high fiber bars in the grocery store, but I'm really trying my best to find a natural source.

Edit: Just wanted to say thank you, everyone, for the helpful suggestions! I see a lot that would be easy for me to implement, and I plan on trying those with my next grocery cycle. Keep the suggestions coming if you'd like, so it can be useful to someone else like me!