Another option would be to add a column in the query editor, that would create one line for each month in both tables. You could then connect these tables by the date (either directly or via a calendar-table):
This formula in an added-custom columnn would create a list on you first table with all months-end-dates within the range:
List.Distinct(List.Transform({Number.From([Health Plan Start Date])..Number.From([Health Plan End Date])}, each Date.EndOfMonth(Date.From(_))))
Simply replace the bolded expressions by the column names of your 2nd table.
You then just have to expand this column and all the rows will be created automatically. Just load to the data model then.
It will drag on the performance, but seems a bit quicker to implement.