Describe what this is, explain why this is appropriate in answering your research question, and justify with support from the literature why this is the most appropriate research design for this study.

Investigation healthcare professionals views on the contributory factors to the development of type 2 diabetes mellitus in the United Kingdom

The purpose of your research proposal is to present the problem you are proposing to investigate, the health problem, to present the reason for studying this (i.e. the gap in knowledge), and for you to describe, explain and justify how you will conduct your study.
The following structure is advised in the guidance:

Where some students go wrong is that they spend too much time explaining the health problem, and not enough time on describing. explain and justifying the research decisions. Make sure you balance this carefully. The emphasis should be on explaining the research methods.
This then also means you need to balance your words carefully. Do not use more than 1000 words on your introduction and literature review, so that you have at least 1000 words left for your methods.

Justifying your research decisions means you support your decisions with literature. For example, you have chosen a qualitative design, describe what this is, explain why this is appropriate in answering your research question, and justify with support from the literature why this is the most appropriate research design for this study.

Make sure to use Harvard referencing and double check if you are using this correctly.
Writing concisely is an important skill and the word count will be adhered to. Word count policy is about fairness between students and students who go over the word count give themselves an unfair advantage over other students.