Preparation:

Prepare rice according to package instructions. 

Microwave vinegar, 2 tablespoons sugar, and salt for 30 seconds to dissolve solids. 
When the rice is ready, pour vinegar mixture over rice and fold gently to incorporate. Allow rice to cool until just warm to the touch. While the rice is cooling, heat the eel to the package’s recommendations. 

Prepare sauce by heating soy sauce, mirin, and remaining sugar (6 tablespoons) in a saucepan until it thickens slightly. Reserve in a ramekin or small bowl. Slice cucumber and reserve. 

To serve, slice the eel in one inch-wide pieces and serve over warm rice with cucumber slices and pickled ginger. Coat eel with additional sauce.