Abstract: An adjustable mounting bracket assembly for a fixture is disclosed for securely mounting a fixture to construction framing and easily enabling adjustment of the depth of the fixture at any time during or after a wall installation process. A fixture mounting bracket assembly includes a mounting structure having a mounting plate and male connectors, and a support structure having a support frame and female connectors. The male and female connectors join the mounting structure and the support structure, providing an adjustable space between the mounting plate and the support frame. The respective connectors can engage with each other through various means, such as a simple peg and hole friction assembly, a screw and screw hole threaded assembly, a rivet and hole assembly, and/or a locking pin and hole array assembly. The bracket assembly is configured to support a fixture.