A mounting assembly for securing a fixture in a desired orientation. The assembly includes a fulcrum and an opposing structure each secured with respect to the fixture and positioned to receive a support member therebetween. The fulcrum defines a fulcrum plane and is positioned to pivotably engage one side of the support member. The assembly also includes at least one adjustable engager separately secured to the opposing structure for engaging the support member at position spaced from the fulcrum plane such that, when the support member is received between the fulcrum and the engager, adjustment of the engager holds the fixture in the desired orientation. In some embodiments, the fixture is a luminaire.