It SHOULD be simple! Welcome to BYC and the thread
You don't HAVE to make it complicated
You can use oats, but most would recommend wheat bran instead, for a variety of reasons. I used a mixture of both, with whole wheat flour added as well. The complete life cycle from egg, to larva, to pupa to beetle can take anywhere from 2-6 months depending on temperature (primarily) as well as other variables. Make sure your container is at least 6 inches from the top of the "food" layer to the top of the container. The sliced apple (or potato, or carrot) is simply for the worms/beetles to get moisture. Depending on how humid it is where you're located, you need to be careful about too MUCH moisture and mold developing. You want to keep the grain food mix from getting wet. Other than that, just check up on them once a week or so
and let them do what they do. Can't be much simpler than that.
Your birds will eat everything in the container including the grains, the beetles, the pupae and the larva (worms). So if you really wanted to, you could just scoop out a cup full and go make your chickens go crazy
or leave the beetles (they lay the eggs) and the pupae (they become the beetles) and just feed worms. Enjoy!
