  The principal objective of this project is to investigate the gravitational
lensing by asymptotically flat black holes in the framework of Horndeski theory
in weak field limits. To achieve this objective, we utilize the Gauss-Bonnet
theorem to the optical geometry of asymptotically flat black holes and apply
the Gibbons-Werner technique to achieve the deflection angle of photons in weak
field limits. Subsequently, we manifest the influence of plasma medium on
deflection of photons by asymptotically flat black holes in the context of
Horndeski theory. We also examine the graphical impact of deflection angle on
asymptotically flat black holes in the background of Horndeski theory in plasma
medium as well as non-plasma medium.
