Clustered index scan in query with non clustered index filter
One way to coax the optimizer to use narrow nonclustered indexes is to use a CTE:

WITH fix_me AS (
SELECT OrganizationId 
FROM Operations 
WHERE OrganizationId = 'some uniqueindetifier'
)
SELECT *
FROM Operations AS o
JOIN fix_me AS f
ON f.OrganizationId = o.OrganizationId


I'm guessing that your nonclustered index isn't covering, meaning the optimizer has a choice between doing a Key Lookup, or scanning the Clustered Index.

Using a CTE in this way can help guide the optimizer to use a narrow index to get only the necessary rows, but may also be ignored.

Since you gave an incomplete picture of your query and table design, feel free to adjust that to fit your needs. 

I talk about this technique more in this presentation:

Improving SELECT * Query Performance