Prepare lentils according to package directions. Combine lentils with mint, vinegar and 4 tablespoons macadamia nut oil. Season to taste with salt and pepper. Refrigerate until serving.
Whisk together mango, miso, mirin, and sake in a small bowl.
Sprinkle fillets with 1/4 teaspoon each sea salt and black pepper. Heat remaining 1 tablespoon macadamia nut oil in wok over high heat. Sear fillets quickly on both sides until browned but not cooked through. Brush fillets with mango-miso mixture, and turn over. Cook fish over medium heat 6 minutes or until just opaque throughout. Serve fillets over lentil salad with tomatoes and watercress.