Cook the pasta in a generous amount of boiling water until just tender, about 8 to 10 minutes. While the pasta cooks, heat the oil in a very large skillet set over medium heat. Add the onion and garlic and cook 3 to 4 minutes. Add the stock, salmon, asparagus and snap peas, bring to simmer, and then reserve on low heat.
When the pasta is cooked, reserve 1/2 cup of its cooking liquid. Drain the pasta well and add it to the skillet along with the 1/2 cup cooking liquid, dill, lemon juice, salt and pepper. Toss to combine, and serve.