In this paper the design of a handheld light applicator for microwave heating is presented. The applicator is made of an array of resonant longitudinal slots cut on a broad wall of a rectangular waveguide, and it is covered by a cylindrical lens made of Plexiglas with a permittivity of 2.53. The geometrical optics approach is used as initial approximation to establish the lens profile. It allows for the shaping of the slotted waveguide's radiation pattern into a desired output pattern in the transversal plane. Three-dimensional simulation results show that the applicator performance can be improved at 2.45 GHz by using a homogeneous dielectric lens.