Into a medium-size pot over medium heat, add olive oil. When the oil is hot, add yellow onion, dried thyme leaves, sea salt, and ground black pepper. Cook, stirring frequently for 2 minutes.
Add Arborio rice and stir to coat. Continue cooking an additional 1 minute.
Add the wine, stirring until liquid is absorbed, about 3 minutes.
Add broth 1/2 cup at a time, stirring until liquid is mostly absorbed after each addition. In about 25-30 minutes, rice will be tender but firm to the bite. Reduce heat to low.
Gently stir in lemon juice, vegan Parmesan cheese, and chopped artichoke hearts. Adjust seasoning to taste.
Sprinkle with walnuts and scallions.
Serve hot.