Add the chicken stock to a small saucepan and heat to a simmer. Turn to the lowest heat to keep the stock warm.
In a large skillet, melt the butter over medium heat. Add the chopped onion and sauté until soft, approximately 3-5 minutes.
Add the arborio rice. Stir and let the rice get a little translucent, about 2-3 minutes.
Ladle in about a quarter cup of the warm chicken stock. Stir and allow to become fully absorbed before adding another quarter cup of stock. Stir mixture frequently and keep an eye on it. The entire process will take about 25 minutes until all the broth has been absorbed.
When all of the stock is absorbed, stir in the thyme, goat cheese, parmesan cheese, lemon juice, lemon zest, salt and pepper. Serve immediately.