Cliff Avril and Marshawn Lynch did one last thing as teammates before Beast Mode headed off to Oakland ... and for the people of Haiti, it's better than anything the men ever did on the field.

Cliff has been down in Haiti building schools with his Cliff Avril Family Foundation, and he talked to TMZ Sports ... telling us it wouldn't have been possible without an assist from Money Lynch.

"Marshawn put me in contact with the right people for building the school."

This is the 2nd year Avril has done it, and he had not only Marshawn, but Michael Bennett and Stephen Tulloch to help him do the heavy lifting.

The trip also gave Avril a chance to look in on the 12 houses he built in Haiti recently ... one for each NFL sack he got last year.

I know these guys are mostly Seahawks, but we gotta say, they seem like Saints.