Bring water to a boil in a saucepan. Add farro and reduce heat to simmer; cook until tender, about 30 minutes.
Meanwhile, melt butter in a nonstick pan over medium heat. Add garlic and cook, stirring frequently, until slightly soft and fragrant, 1 to 2 minutes. Add mushrooms and season with onion powder, garlic salt, and pepper. Cook over medium-high heat, stirring frequently, about 10 minutes.
Drain and discard any excess water from the farro; add farro to the pan with the mushroom mixture. Add chicken stock and increase heat to a simmer, stirring frequently, about 5 minutes. Add Parmesan cheese and stir until melted, about 1 minute more.