In this paper we model second-harmonic generation in a microphotonic structure using two different numerical methods. The proposed two-dimensional waveguide device is challenging as it incorporates a high-contrast grating, which instigates strong local enhancement but also radiation losses. The first simulation method extends the time-domain beam propagation method, whereas the second one builds upon frequency-domain eigenmode expansion. Good agreement between both tools is obtained for both the linear and nonlinear simulations.