Heat olive oil in a large saucepan or Dutch oven over medium heat. Add onion and saute until cooked and translucent, stirring frequently, about 8-10 minutes. Add garlic and saute for a further 2 minutes.
Stir in mushrooms and thyme or sage and cook, stirring occasionally, until mushrooms are tender and browned, about 5-6 minutes.
Stir in rice, lentils, salt and pepper and broth. Bring to a boil then cover and reduce to a very low heat and gently simmer until rice is cooked through, about 20 minutes. Stir in butter and allow to melt.
Remove from heat, stir in parsley and serve.