Real aperture radar (RAR) has a limited aperture of the antenna resulting in a low azimuthal resolution. To improve the azimuthal resolution, the L2 regularization method is applied to the forward-looking scanning radar imaging. However, the traditional L2 regularization method requires an inverse operation, which results in extremely low imaging efficiency. In this paper, we propose a fast frequency domain approach based on Gaussian prior for forward-looking scanning radar imaging. This method transforms the spatial domain inverse convolution problem to the frequency domain and avoids matrix inverse. The fast Fourier transform implementation greatly improves imaging efficiency. The simulation experiments demonstrate the effectiveness of the proposed method.