Well, I tell you, it takes a lot of practice to teach yourself to do good research. But you can always start with, for example, going to several sites that give you diet information in general (places like Wikipedia, The World Parrot Trust, etc.) and see, exactly WHERE they come from and what are the native plants they feed on. I had a little list saved from way back when I had ekkies and got the below info from somewhere: Pandanus (screw pine), nonda plum, red beech, grewia papuana burret, mackinlaya, pirrungu, hopbrush, micromelum minutum, dissilaria laxivernis, brittlewood, nasturtium tree, zyzygium bamagenese, sarsaparilla tree, solitaire/livistona/dicksonia palms, small-leaved fire vine, crepe myrtle and cinnamonwood tree. Then you look up each plant and try to find out what kind of nutrition they would get from it.
But, saying something like 'parrots don't eat cooked rice in the wild' doesn't really signify and I'll tell you why. The truth of the matter is that, unless you not only live in the same country where the bird comes from but also in an area where the flora has been completely unchanged by civilization, you won't be able to feed the bird its natural diet. So, the only solution is to get an accurate idea of what the basic nutritional parameters are and try to stay within the ranges as much as possible. This is a problem because we really do not have an idea of what most species basic nutritional parameters are and, if we did, we would also need to know in which season this parameters are valid because, for example, we know that amazons feed on a maximum of 17% protein BUT only during breeding season when they are feeding their babies PLUS these are birds that are exposed to the elements, which need to fly miles to find enough food, which might get 17% one day but only 12% the next, etc. Because, that's another kicker with birds: there isn't a single one that actually gets a complete balanced meal every day! NONE! Birds often go to sleep hungry during the resting season and, even during the spring or dry season or whatever the plant growing season is called in their part of the world, they don't eat a bit of this and a bit of that so as to ensure they are getting a balanced meal. Nope! Birds find, say, a fig tree and eat from it until all the figs are gone -something that might take 2 or 3 days for a smallish flock so, during those three days, all they eat is figs! Because nature made it so the 'balance' in their nutrition is achieved through all these ups and downs in their feeding ecology. It's only man that thinks that eating a balanced meal every single time is the way to go - not Mother Nature.
Now, as to cooked grains been unnatural to birds - yes, they are. But then everything we feed them is unnatural so the concept behind cooking the grains is that it makes them more digestible (both in terms of complex carbs AND protein). I don't cook them all the way through, I leave them al dente (soft in the outside but still hard inside) - I've done a lot of research on this subject and I feel that this gives them the best of two worlds: the hardness and 'naturalness' of the grain along with the better digestibility through the cooking AND, let's not forget a VERY important 'side effect' of cooking grains: it infuses them with water, making the meal much more similar (in terms of moisture content) to what they would be eating in the wild! And this high water content is also great because you don't have to worry too much about feeding too many carbs as their crops get full with less carbs so, no matter how much gloop you feed, the bird never becomes overweight, a very common problem with pet birds that are free-fed pellets or seeds! People try to manage their weight by actually counting the number of pellets they feed the bird but I hate the idea of any of my birds been hungry, not finding any filling food to eat and having to wait until either their dinner or the next day... Feeding gloop is so much better for them and so much easier for me that I really don't see any benefit in switching -by the way, I've been feeding all my birds gloop for over 20 years now and they all do wonderfully on it: good blood work (even the ones that came to me with liver or kidney issues), good weight and, most importantly, they can eat as much as they want and they all love it!
A couple of links for you to read about this subject:
https://www.verywell.com/what-you-need- ... es-2242228http://www.beyondveg.com/tu-j-l/raw-coo ... d-2a.shtml