Yes, DISCUSSED is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, S 1, C 3, U 1, S 1, S 1, E 1, D 2.

Is it a valid word?

DISCUSSED is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

to consider or examine in speech or writing
speak with others about (something); talk (something) over in detail; have a discussion

Also: talk about, hash out, talk over.