Please keep in mind that there can be a significant difference between how a fish assimilates and utilizes
aquatic based plant matter in the wild, and how a fish assimilates and utilizes
terrestrial based plant matter in captivity.
Science has proven that at least with most species of fish studied to date, terrestrial based plant matter can potentially cause health issues, especially if fed in a raw unprocessed state, due to the anti-nutritional matter found in the vast majority of terrestrial based plants. Not a major problem if one is feeding limited quantities, but can cause some serious problems in at least some species of fish when fed at higher levels on a regular basis.
http://www.fao.org/docrep/003/t0700e/T0700E06.htm
Soybeans contain saponins which at higher levels have proven to cause damage a fishes intestinal cells. Peas contain phytic acid, tannins, and trypsin inhibitors, which again are not something that fish benifit from and can potentially cause negative health issues when fed in excess. Check out the list in the link above & be informed, not all plant matter is going to offer a nutrient boost for fish.
If one is wanting to increase the amount of plant matter in their fishes diet, my advice has always been to offer fish aquatic based plant matter. The fact that a fish enjoys eating something, doesn't necessarily mean that it's good for them.