  In this paper we build the general formalism of gravitational lensing in
luminal Horndeski theories, deriving the Jacobi matrix equation and the general
angular diameter distance in these theories through the screen space formalism.
We generalize the focusing and multiple lensing theorems to include Scalar
Tensor theories belonging to the class and derive constraints they must satisfy
to exhibit the same gravitional lensing behavior predicted by General
Relativity. This provides a way to test theories through Strong Lensing
effects, as well as a full theoretical framework for testing lensing in these
theories. We find that for some subclasses, like metric $f(R)$ and unified
$k$-essence, the conditions are satisified in general physical cases, while for
others like Galileon Condensate models, the conditions impose constraints on
the parameter space of the theory.
