Is there a seasoning out there that can add fiber to a meal?!
No but metamucil will. What are you trying to cook this question is hard to answer. If you are making pasta use whole grain noodles. If you are have a bread in your meal, make sure it's whole grain. Eat fruits and grains as close the natural state as possible.
Ground flax will. It doesn't have much of a taste but it mixes into things well.