In this paper, we present data on the transition from the lamellar (L-alpha) to the gyroid inverse bicontinuous cubic (Q(II)(G)) mesophase. The system investigated was 2:1 lauric acid (LA)/dilauroylphosphatidylcholine (DLPC), at a fixed overall hydration of 50% water by weight. The phase transition was induced by a pressure jump and monitored by time-resolved X-ray diffraction (TRXRD). We observe the gradual appearance of signals from the emergent Q(II)(G) phase and an accompanying disappearance of signals from the initial L-alpha. phase. These changes correspond to a transformation occurring over a time scale which varies between seconds and minutes. We further observe that the lattice parameters of both the initial L-alpha and final Q(II)(G) phases change throughout the transformation. We suggest that this reflects a competition between the two phases for the limited amount of water available. In addition, we suggest a mechanism whereby the transformation from L-alpha to Q(II)(G) proceeds via an intermediate phase, which we suggest is the diamond inverse bicontinuous cubic phase (Q(II)(D)). We present evidence for its identity and suggest Q(II)(G) mechanistic pathways for its formation from the L, phase and subsequent transformation into the phase.