不用加,并且和时态没有关系,其实就是一个定语从句：We are going to talk about the problem which we discussed at the last meeting.而在这,先行词problem在从句中作宾语,所以根据从句的规则,先行词作宾语时,关系词（which、that）可以省略（当然也可以不省略的）,所以这句话discussed前应该加主语we：We are going to talk about the problem we discussed at the last meeting.而又因为逻辑主语和主句主语一直,都是we,所以在惯用法中逻辑主语省略了,就成了：We are going to talk about the problem discussed at the last metting.加being 搂主理解为被动语态,但是不能理解为被动语态：we are going to talk about the problem which was discussed at the last metting.因为如果是被动语态,那就什么都不能省略了,必须写全了,除非是分词作状语,而这又不是,这是个定于从句,所以要这样理解.
还详细否?