You already eat beans sometimes so make them a part of your life! I keep a bean salad around a lot of the time, like a cowboy caviar. It’s easy to have a little half cup scoop at breakfast, lunch and dinner and over the day that’s 9-21 grams of fiber, depending on the bean you use.
Either that or this:
https://www.mynewroots.org/site/2013/02/the-life-changing-loaf-of-bread/ It’s “bread” like so many holistic foods are what they claim to be, but it is fiber city. Add salt, for the love of Pete. It needs it. And it says “makes the best toast” - more like toasted is the only way to boost the flavor.