For nutrients and fat at least I sneak hemp hearts (seeds) into my little guys rice that should also help with digestion. Anything with fiber so fruits and smoothies
I started giving my daughter a little bit of dissolved magnesium powder in juice/water every other day. It's made world of a difference. Adding fiber never seemed to help her in comparison. Double check with your pediatrician if they would recommend trying that approach.
miralax
maybe try making it a sauce and adding it to noodles or something my daughters becoming picky too she loves veggies! but i’m having trouble with her eating any meals even when we go out