For the beef and dressing: Prepare a grill or grill pan for medium-high heat.
Season both sides of the steak with salt. Grill until medium rare, about 4 minutes per side. Set aside.
To make the dressing, combine the ponzu (or soy sauce), sesame oil, olive oil, vinegar, brown sugar, ginger, hot chili oil and garlic in a bowl. Mix to combine, then taste and adjust the flavors/seasonings.
When the steak is cool enough, place in a large resealable plastic bag. Add 3 tablespoons of the dressing. Seal the bag tightly and place in the fridge until needed.
Bring a pot of water to a boil and cook the noodles according to the package directions. Drain and place in a bowl. Pour the remaining dressing over the top and toss to combine. Finally, toss in the green onions. Cover the bowl with plastic wrap and refrigerate for at least a couple of hours or until cool. You can make the steak and noodles well in advance of when you want to serve them.
For the peanut sauce: Heat the vegetable oil in a small pot over low heat. Add the curry powder, garlic, shallot and ginger and cook until the aromatics soften, about 5 minutes.
Scrape into a blender and add the coconut milk, soy sauce, brown sugar, peanut butter, hot chili oil, lime juice and a pinch of salt. Blend, adding hot water as needed a little at a time to thin it and make it smooth.
To serve, slice the steak against the grain into thin strips. Drizzle a little ponzu (or soy sauce) over the noodles, just to give them a little flavor boost, throw in the chopped cilantro and toss to combine. Serve the strips of beef over a mound of noodles, or throw it all into a bowl together. Put some of the peanut sauce into small bowls and serve on the side--to be poured over when you eat.