An innovative mixed-methods approach to exploratory focus group design is presented using a case study conducted with smallholder rice farmers in Vietnam. Understanding human decision-making under the uncertainties of a complex and changing social and environmental context requires a flexible yet structured and theoretically grounded approach. Using Bayesian belief networks as the architecture of our model allows the study to incorporate both qualitative and quantitative data, the former gathered at this stage in a participatory focus group setting and the latter to be collected in a subsequent survey. This framework further lends itself well to incorporating systematic behavioral approaches to decision-making analysis using Ajzen's theory of planned behavior framework, a symbiosis that remains underexplored in the literature. The visual nature of the networks makes them easily accessible to participants, and the proposed technical solutions to field implementation are flexible, inexpensive, and shown in practice to mitigate issues of co-moderating discussion across language barriers. The tools and methods described are transparent, reproducible in comparative contexts, and transferable to a range of research topics and questions.