You will need Mighty Thistle and Amoranth in Hyrule Warriors: Age of Calamity to complete the “A Feast of Greens” cooking quest. You’ll need a total of five Mighty Thistle, five Amoranth, and five Hyrule Herb to make the required recipe.
The game is pretty loath to explain how you actually get these, however, so we are here to help you get a decent collection for your larder. To get both Amoranth and Mighty Thistle, you will need to cut grass. It might sound strange, but levels are covered in grassy areas, and what you may have thought were drops from enemies are actually from chopping the grass while you fight.
Both resources drop from chopped grass, so if you make your way to Hyrule Field and go ham with your sword you will be able to farm them. They are rare though, Hyrule Herb is the most likely drop, along with various types of lizards and other creatures, but if you do it for long enough you will get some Amoranth and Mighty Thistle to drop.
If you really want to get this quest wrapped up, remember that you can replay any mission, so if you want to get a bit more powerful, then come back and quickly blow through the quest while farming for Amoranth and Mighty Thistle, that is definitely an option.