If you have to go that way (I do not know any other way) first you need to create a NSQL query to get the fields you need.
Something like
where you have the investment id which you need for the filter. Then go to the query attributes
Double click the ID field (I've relabeled it u_id)
Change the Extended Data Type to Lookup - Numeric and select the lookup Project browse.
Include the u_id in the filter of the query based portlet layout and open the filter field properties.
Re-label the field as you like eg. Project or Project Name
Then that field should look like this
When you browse the filter (click the binoculars) you see what is defined for the lookup.
That is the label Select Projects the displayed fields and the filter filter fields
If that is not good for you you should manually create a copy of the lookup and modify what you need as the Project Browse is a system restricted lookup and used also elsewhere and therefore should not be modified.
The filter field properties was set to single select so only one value can be selected. Once you have made your selection click Add and in the portlet Filter.