A double-cavity microwave oven is disclosed that includes a first and a second cooking cavity, a moveable barrier disposed between the first and the second cavity, a first and a second magnetron, and a first and a second waveguide corresponding to the first and the second magnetron, respectively. The first cavity is electromagnetically isolated from the second cavity, and, as the barrier moves, the size of the first cavity relative to the second cavity changes. As the barrier is in a first position, the first waveguide directs microwaves from the first magnetron to the first cavity and the second waveguide directs microwaves from the second magnetron to the second cavity. As the barrier is in a second position, the first and the second waveguide direct microwaves from the first and the second magnetron to the first cavity. Various embodiments are also disclosed including additional features.