1. Cook the noodles in boiling water until soft (about 6 minutes for soba, 8 for spaghetti). Transfer with tongs to a strainer. Add asparagus to same boiling water. Cook until al dente (about 2 minutes); rinse under cold water.
2. Heat a grill pan or skillet over medium-high heat. Coat lightly with cooking spray. Cook the salmon until cooked through, turning pieces (about 2-3 minutes per side). Reserve.
3. Make the vinaigrette: Whisk together sesame oil, lime zest and juice, and salt and pepper in a small bowl. Combine the noodles, asparagus, and vinaigrette in a medium serving bowl.
4. Add the cucumber and avocado; toss to coat. Just before serving, add salmon. Serve warm or at room temperature, or make up to 4 hours ahead and keep refrigerated in an airtight container.