Whisk together 1/4 cup of the oil, five-spice powder and garlic in a medium baking dish, add the lamb and turn to coat in the mixture. Cover and refrigerate for at least 1 hour and up to 4 hours.
Whisk together the vinegar, soy sauce, sesame oil, sugar, jalapeno, honey and remaining 2 tablespoons canola oil in a large bowl and let sit while you prepare the noodles.
Bring a large pot of salted water to a boil. Add the soba noodles and cook until just tender, approximately 5 minutes. Drain well, place in the bowl with the dressing, add the green onions and cilantro and mix until combined. Let sit at room temperature while you cook the lamb. Can be made 8 hours in advance and refrigerated. Serve at room temperature or cold.
Heat the grill to high.
Remove the lamb from the marinade and season with salt. Place the tenderloins on the grill and cook until golden brown and slightly charred, 3 to 4 minutes. Turn over and continue grilling for 2 to 3 minutes for medium-rare doneness. Remove from the grill, let rest for 5 minutes before slicing into 1/4-inch thick slices. Transfer noodles to a large platter and top with the sliced lamb.
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