I was reading about Penn State's "Lean & Green Research Initiative." Under the heading "Methodology and [P]rocess," they say this: "We apply VALUE-ADDING and WASTE-REDUCING strategies throughout the life cycle of planning, managing, design, construction, and operation of capital facilities." (I capitalized the relevant words.) http://www.engr.psu.edu/leanandgreen/research_program.aspx
So in addition to "energy saving and environmental compliance" (the "green" part), I would interpret "lean" as describing a business that is run efficiently also with regard to personnel and operating policies and procedures.