I'm trying to say "sushi was my favourite food because it was very delicious," and I'm not sure if it is すしがーばん好きだからとてもおいしかった。or if it is すしがーばん好きだっただからとてもおいしかった。
Any help would be appreciated
You have the order reversed. In English we say "<effect> because <reason>", but in Japanese it's "<reason>から<effect>." The result is that your sentences currently say "The sushi was delicious because I loved it", which doesn't make much sense.
As for the difference between the two tenses, おいしかったから is used for a specific past experience (e.g. the sushi I ate in Japan was delicious), and おいしいから is for its general taste you usually feel.
If you mean "I hadn't liked sushi but became to like it after eating a delicious sushi" by "I didn't like it", you need to use another expression to explain it.