I feed a basic diet of Harrison's pellets, fresh veggies and fruits, dried fruits, seeds and nuts, cooked pasta, beans and veggies and a few treats of things like Nutriberries or AviCakes. Depends of what kind of parrot it is exactly what kind of mix of the aforementioned foods I give each bird. Cockatiels are basic seed eaters in their native Australia; so my tiels get fifty percent Harrison's Lifetime Fine Pellets, twenty five percent seed/dried fruit/nuts, ten percent fresh veggies and five percent cooked pasta, beans and veggies. Most my other birds get less in the way of seeds and dry fruit and more in the fresh veggies and fruits.
Everyone has their own belief about what is healthy for a parrot to eat and it is noted in the last thirty years that the quality of the diet is crucial to the lifespan of a bird. The better the diet, the longer they live and the healthier their life. I feed Harrison pellets, Roudybush pellets and a small amount of Zupreem Fruit Blend. I have cut back on the Fruit Blend because of the amount of sugar in it. But most pellets are healthy formulations for parrots, you just have to decide what level of fats, sugars and proteins you want in your pellets and what your own bird finds as an attractive and tasty diet. Ninety percent of my parrots prefer Harrisons pellets, but the other ten percent prefer Roudybush; I try and make sure what they prefer to eat is what I provide. It is funny to watch the individual parrots shop the foraging stations in the birdroom picking out what they want to eat that day. The only thing I leave in their cage overnight for snacks and first thing in the morning eating is pellets; that way I know they are getting complete nutrition in each bite for at least part of the day. For the rest of the day they are loose in the birdroom and able to pick and choose from the foraging stations and please themselves.
It seems to work because my birds are healthy and maintain good weight on their own.