A BTS would probably eat anything you gave them, but it doesnt necessarily mean its healthy.
i nthe case of goldfish, they are quite fatty, and goldfish which you havent bred yourseld likely contains a variated mix of chemicals from where it grew up - fatty fish store chemicals in their body fats.
another argument on this forum is, that BTS does not eat fish in the wild. they eat dead animals and veggies and fruits and insects and such, but never fish.
i do not think it is harmful to give fish once as its usually quite nutricious, but im not sure it is a good idea. its hard to tell if they feel bad from what they eat.
the diet otherwise sounds good, however you could probably exclude the insects if you give them to him since hes a juvenile bts, dog food is much more protein rich and with veggies its without doubt great for any bts at any age

although dubia roaches are great staple feeders along with dogfood too. mixing is always good.
do keep in mind the fruit is a treat

no matter if its an adult or a juvenile, it is not recommended to be fed at every feeding.