Go to Students > Enrolment > Statistics and the report will automatically default to only showing today's data. Click into the filters, and select to show data by Ethnicity.
You'll then see the number and percentage of your students that fall into the different ethnic groups.
If you want to see only certain groups, click into the filters, and select these from the Students who are box. You can see more information on the available ethnicities to select here: Add ethnicity and ethnicity source for students
Top Tip: To find your BAME percentage, you'll need to add up these numbers, then divide by the number of students enrolled at your school.