honestly...I'm not a genius, and I havent done a dissertation, but I hear they're usually 20 pages or so, so I have done papers and reports before that were nearly that long.
It's all about the outline bruh. The power of the outline.
What you do is...set up the right question/thesis.
Then build the paper with questions to answer or describe the thesis
Then do the research question by question, and answer each with a couple paragraphs/pages, and citations, remembering your purpose for that question, and towards the thesis
Then have subtopics. Title them throughout the paper, kind of like chapters to a novel. It's just sections/parts of your paper.
Also to fill in pages, provide other sources like surveys, charts, but minimally compared to the amount of text/words.
There you go really. I've surprised a whole hell of a lot of teachers and lecturers over the years and that's my formula/process really.