I have only had my GT for about a month but I always feed my cichlids for the most part the same thing. I feel like your cichlid will get the best diet from a variety of foods. I always use a cichlid pellet, cichlid sticks, flake, shrimp pellets, krill and some times tubifex worms. I will also from time to time get some earthworms from one of my friends that raises his own.
When it comes to how often you should feed your fish I always feed mine when they are young 2-3 times a day. Once they get to be about full grown I will reduce it down to only once a day. Hope this helps and good luck with those GT's they already look great.
I agree , good quality pellet food as a staple and frozen foods as a supplement once or twice a week. I feed mine Omega one pellets about 2-3 a day with occasional brine shrimp and blood worms. I will say though that your gonna want a bigger tank eventually, cause those guys are gonna outgrow that tank before long.