Which of the seven si units would you expect to be part of the definition of a lumen?

The seven SI units are: kilogram, meter, second, kelvin, mole, ampere and candela.

Out of these seven, the one that will probably be part of the definition of a lumen is candela.

The luminous intensity of a light source is the the luminous flux emitted by that light source in a unit solid angle. The SI unit of luminous flux is lumen and the SI unit of luminous intensity is lumen divided by steradian [lumen/steradian] which is called Candela.