500 grams? Wow, that's quite a bit, but hey - if you're gaining weight, that's great! ;)
To clarify, do you mean 500 grams when raw (i.e. the dry grains), or 500 grams when cooked (i.e. when plump and moist)? Also, how are you cooking these grains? I've tried quinoa a handful of times in the past, but was never sure if it was completely cooked - there was still water left in the pan.
I eat 75 grams of germinated brown rice + 50 grams of split mung beans each day (I weigh the quantities into my rice cooker), adding garlic, vegetables, spices, and a little oil to make a kind of Indian kitchari, which I eat for lunch.