In a large saucepan, bring the vegetable stock to a simmer and keep it on low heat.

In another large saucepan, melt the butter over medium heat. Add the onion and cook until softened, about 5 minutes.

Add the garlic and cook for another minute. Add the mushrooms and cook until they release their liquid and it evaporates, about 8 minutes.

Add the rice and stir to coat it with the butter and mushroom mixture. Cook for 1-2 minutes, stirring constantly, until the rice turns opaque.

Add a ladleful of the simmering vegetable stock to the rice and stir until the liquid is absorbed. Repeat, adding one ladleful at a time, until the rice is cooked through but still al dente, about 25-30 minutes.

Stir in the peas, Parmesan cheese, and salt and pepper to taste. Cook for another 2-3 minutes, until the peas are heated through and the cheese is melted. Serve hot.

Garnish with herbs and additional Parmesan cheese, if desired.