Rinse the rice under cold water until the water runs clear.
In a medium saucepan, heat the olive oil over medium heat.
Add the diced onion and sauté until translucent, about 5-7 minutes.
Stir in the minced garlic and cook for an additional minute.
Add the sliced mushrooms and cook until they release their moisture, about 5-8 minutes.
Stir in the rinsed rice, toasting it briefly for about 2 minutes.
Pour in the vegetable or mushroom broth and season with salt and pepper.
Bring the mixture to a boil, then reduce the heat, cover, and simmer for 15-20 minutes.
After cooking, remove from heat and let it sit covered for an additional 5 minutes.
Fluff the rice with a fork and garnish with fresh parsley.