In a large skillet, heat cooking oil over medium heat. Saute onion for 3 minutes, add leeks and Chinese cabbage. Cook for 10 minutes more (or until soft). Season with thyme, pepper and salt. Sir regularly.
Meanwhile, cook spaghetti according to the package in lightly salted water.
Blend all pesto ingredients until smooth.
Combine pasta, leek mix, and pesto. Give it a good stir and serve.
Note: if too dry, add a little splash of pasta cooking water.
Optional: add crushed walnuts on top for extra crunch.