Meaning of "になっていて"?

the sentence is "Xになっていて"
I think it roughly means "it becomes X" but I want to know the correct grammar/tense.

Thank you in advance!

Have you learned the function of the -te form and -te iru form?

I know -te iru makes it a continuous tense but.. I feel weird using "it's becoming X" (X is a noun: 二重構造)
maybe there's a better english translation, just curious.

edit: oh wait it's even natteite not natteiru /slap

Of course. I mean なっていて is the -te form of なっている.
The present progressive is just one of the functions of the -te iru form, which is basically for durative verbs. なる is a punctual/instantaneous verb, so なっている expresses the current state that results from prior movements (= なった).

Our discussion in the following thread and the pdf file linked in the thread would be helpful to understand the concept of the -te iru form.
https://jref.com/threads/います-ています.55658/