Lighting retrofit systems and methods are disclosed that can be used with different light fixtures, but that are particularly adapted for use with retrofitting troffer-style fixtures with LED based light engines. The retrofit systems being assembled without disturbing the lighting or troffer pan or housing (“troffer pan”) for the lighting system being retrofitted. Some of these embodiments can comprise a mounting fixture or frame that can be mounted in an opening in a ceiling grid, and held in place between the grid and the troffer pan edge. The fixture or frame can comprise an opening for a light engine, with the engine being quickly and easily connected to electrical power in the troffer pan and then mountable within the frame opening. These embodiments can allow for the quick and easy construction of the retrofit system without the need for adhesives and fasteners such brackets and screws.