Prepare the Eggplant: Start by slicing the eggplant lengthwise into long strips that resemble traditional unagi fillets. Lightly score the flesh in a crosshatch pattern without cutting through the skin. This simple step helps the eggplant cook evenly and allows the vegan unagi sauce to soak in, enhancing flavor.
Make the Marinade: In a small bowl, whisk together vegan soy sauce, teriyaki sauce, and vegan fish sauce to create a rich, savory marinade similar to classic unagi sauce. Brush the mixture generously over the eggplant strips, coating both sides so they absorb the sweet, savory flavors.
Pan Cook the Eggplant: Heat a thin layer of vegetable oil in a non-stick pan over medium heat. Place the eggplant strips, skin-side up, in the pan and cook until the flesh is golden and tender. Flip the strips and continue cooking until the skin side lightly crisps. Brush or spoon more marinade into the pan as the eggplant cooks so the sauce thickens and coats the surface with a glossy glaze.
Serve the Eggplant Unagi: Once the eggplant unagi is tender and caramelized, transfer it to a bowl of warm rice. Spoon any remaining sauce over the top, then finish with chopped spring onions and a sprinkle of sesame seeds for a flavorful vegan unagi don.