Make the pickles: In a bowl, combine the vinegar, honey, sesame oil, fish sauce and sriracha, whisking until the honey is dissolved. Fold in the sliced vegetables until fully coated, adding more vinegar to cover fully. Marinate for 24 hours before using.
Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions. Drain the pasta, return to the pot, and drizzle with olive oil.
Combine the lime juice, peanut butter, soy sauce, curry paste, coconut milk, sambal and brown sugar in a bowl with a whisk.
Add the sauce to the noodles, along with the carrots, green onions, peanuts, cilantro and sesame oil, and toss to coat thoroughly. Season with salt and pepper.
Combine all of the marinade ingredients except the canola oil in a blender. Purée until smooth, adding water if necessary. Drizzle in the oil with the motor running until emulsified. Season with salt and pepper.
Divide the marinade in half and brush the tuna steaks with half of the marinade. Sprinkle with salt and pepper.
Heat a grill or large skillet to high heat and sear each side of the tuna for 1 minute, until browned. Slice on the diagonal.
To serve, divide the peanut noodle salad between bowls. Top with seared tuna, pickles and drizzle with reserved marinade.