The toxic foods lists can be a bit deceiving and there are many nuances involved. There are a billion differnt lists and some of the foods that appear on one authority's forbidden list appear on another's recommended list. It can make you crazy. I like to use the rule that if I can eat the food in the form that it is offered, then my bird can likely eat it. The exceptions are avocado, chocolate, caffiene and alcohol, and even those are basically dosage related.
Because I am driven insane by poor/inconsistent information, I've tried to study up on the reasons behind foods appearing on one list or another. Here is a grab bag of what I have found out. Raw alliums (onion, garlic) can interfere with absorption of other nutrients and are best avoided. Salt is another dosage issue, best to avoid significantly salted foods entirely as salt is ubiquitous. Mushrooms are not a problem "because they are a fungus", they are a perfectly nutritious food. The problem is that they spoil easily and most fresh mushrooms you will find in the grocery are already beginning to spoil, so it is safest to avoid them. If you offer pasta with a commercially prepared sauce containing mushroom it is unlikely to be toxic, but watch the salt content! Raw red kidney beans and their close relatives are also toxic for humans. They can cause serious issues due to a chemical that is common in many beans but occurs in very high concentrations in red kidney beans. They should be avoided both raw and in sprouting mixes, but you will rarely see them there for that reason. The beans in sprouting mixes, although raw, are safe to feed either cooked or sprouted. Cooking destroys the chemical that causes the issues. Stone fruit pits and appleseeds are bad for birds and people alike -- again think dosage. Actually, the typical issue with stone fruits is that if you "break" the seed and then expose it to an enzyme in the flesh, you can wind up with a cyanogenic compound. So best to remove the pits. Commercial sprouts can be risky for the same reason mushrooms are, they are often spoiling by the time you get them. Spinach appears on some bad lists because too much of it can cause significant dietary imbalances. Raw tomato also appears on some bad lists because of its high acid content, which is significantly reduced by cooking. Small amounts are unlikely to be a big deal. Peanuts -- yep, peanuts -- are on many bad lists because the shells often harbor a fungus that produces a toxin. The same is said to be true of walnuts. And rhubarb isn't something you'd eat raw, it's not good for birds raw either.
You can actually make yourself crazy like this!
IMHO, at the end of the day, dosage is a BIG deal. Your conure will weigh less than 100g which is about 600 times less than what you weigh and toxic dosages will scale by at least that much! Birds are also more sensitive even than the weight scaling in some cases. You can poison a person with about six pounds of chocolate, but the equivalent dosage for a bird is so much less it is better to just avoid it. This applies for alcohol, salt and caffiene. Scooter has stolen sips of things from glasses which he should not have, but has lived to tell the tale. Free access might not end up so well.
Gee, I've only been on here a few days and I think I've already run out of most of my favorite soapboxes. I hope someone finds this useful...