I should refrain from giving them normal meat. Chicken doesn't necessarily contain a lot of fat but I would stick to proper fish food.
You could feed your Oscars twice a day on various foods. Pellets, frozen foods from the fish shop, worms and insects from your garden. I shouldn't bother with flakes now, Oscars need something a little more substantial.
Bear in mind that my advice is based upon keeping Oscars in a suitable size tank. If you are keeping your Oscars in a very small tank, feeding them twice a day will only add waste to the water a lot. For instance, I would advise someone keeping an adult Oscar and a 55 gallon tank to feed it once a day. You could even feed it every other day and it would be perfectly okay.