In a large pot, heat the olive oil over medium heat. Add the diced onion and sauté for about 3-4 minutes until translucent.
Add the minced garlic and sliced mushrooms to the pot. Cook for another 5-7 minutes, stirring occasionally, until the mushrooms are tender and have released their moisture.
Stir in the rice, dried thyme, and dried parsley. Cook for 1-2 minutes, allowing the rice to toast slightly.
Pour in the vegetable broth and season with salt and pepper. Bring the mixture to a boil.
Once boiling, reduce the heat to low, cover the pot, and let it simmer for 18-20 minutes, or until the rice is cooked and has absorbed the liquid.
Remove the pot from heat and let it sit, covered, for an additional 5 minutes. Fluff the rice with a fork before serving.
Garnish with fresh parsley if desired.