Heat olive oil in a large stockpot or Dutch oven over medium heat. Add garlic and onion, and cook, stirring frequently, until translucent, about 2-3 minutes.
Stir in mushrooms, Worcestershire and thyme and cook, stirring occasionally, until mushrooms are tender and browned, about 5-6 minutes; season with salt and pepper, to taste.
Stir in brown rice and vegetable broth. Bring to a boil; cover, reduce heat and simmer until rice is cooked through, about 40-45 minutes. Stir in butter until melted, about 1 minute.
Serve immediately, garnished with chives, if desired.