Use a spice grinder or pestle and mortar to crush the sesame seeds, then stir in the soy sauce, oil, 1 tbsp of water and a splash of rice vinegar, to make a creamy dressing, season and set aside.
Bring a pan of salted water to the boil, add the noodles and cook following pack instructions, then drain and set aside. Using the same pan, tip in all the spinach and cook until reduced down and dark green. Tip in the noodles, along with the sesame dressing and a splash of water and toss well to heat through.
Heat the oil in a non-stick frying pan over a medium to high heat. Season the skin of the seabass, then place in the pan skin-side down, fry until the skin has crisped up and the flesh has nearly all turned opaque, around 3 mins. Flip over and fry for 30 seconds further, until the fish is flaking and cooked through. Divide the noodles and greens between two bowls and place the fish on top. Scatter over the toasted sesame seeds and serve.