53-year-old Luhnow -- who was hired by the Astros in 2011 -- says he signed a deal with the team in 2018 that included $31 million in guaranteed compensation in addition to performance bonuses.

But, when the team fired him for cause following an investigation into allegations the team conducted a high-tech sign-stealing system in 2017 ... Luhnow claims he got screwed out of a ton of money, more than $22 million.

In his breach of contract lawsuit, Luhnow claims the Astros fired him "even though [he] had no knowledge of -- or involvement in -- the sign-stealing schemes."

He adds, "Yet everyone above and below Luhnow in the Astros organization came away unscathed" -- including the "video room employees who conceived and orchestrated the sign stealing system."

Luhnow claims the "investigation" -- which he puts in quotes in his suit -- was "deeply flawed" and wrongly made him a scapegoat, claiming he had knowledge of they scheme.

"The truth is the Astros had no basis to fire Luhnow, a respected executive with an unblemished record and a 16 year history of compliance with MLB rules."

The Astros fired Luhnow in January 2020 -- after the MLB report was released.

He was hit with a 1-year ban -- same as manager A.J. Hinch -- but Luhnow has not been hired by another team.

Hinch, on the other hand, was just hired to manage the Detroit Tigers.