This paper introduces an approach using the Generalized Luneburg Lens as a modular design element to shape automotive RADAR antennas at mmWave frequencies. An optimization routine that includes unwanted effects associated with manufacturing constraints is presented by adding mechanical constraints in the lens design and using a full-wave solver with the feeding antenna. Two lenses are designed; the first increases the directivity from 14.1 to 15.7 dBi, while the second increases the HPBW of the antenna from 57.6 to 129.6 degrees, demonstrating the flexibility of the presented approach.