Put any of those veggies or all of them together in a blender/food processor with about a half of a cup of water and puree. (Garlic would do good here, adding an immune-boosting agent to the food.)
Mix 1 small packet of unflavored gelatin into veggie puree.
Freeze in ice-cube tray or some other small container of the sort.
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You could go as far as making an all-around food by adding a can of crab meat or fresh/frozen non-oily fish to the mix or even some small shrimp from your grocery store.
When feeding you can either shave bits off, swirl the cube in the tank, or even just submerge cube and rub it gently with your thumb or fingers to get small bits off.
Our fish go wild and it takes 15 minutes a week for me to make enough to feed 2-3 feedings that week for 160 tanks each time. So in 15 minutes I make 320-480 tanks worth of the stuff.
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If you want the easy way out that takes less time you can feed veggie flake or mix flake foods, algae pellets, etc.
I made fish food today with hair algae, left-over kale, crab meat, tilapia meat, garlic, and water. (The kale had sat in fish tanks for 3 days and was what was left uneatten, so they will eat it this coming week.

) (Kale is awesome for a slow to breakdown vegetable for plecos, otos, etc.)