Melt butter in a large skillet over medium-high heat. Cook and stir green onion in hot butter briefly, then add rice. Cook and stir until rice is toasted, 2 to 3 minutes. Pour in water; season with chicken bouillon and pepper. Bring to a boil, then reduce heat to medium-low. Cover and simmer for 20 minutes.
Remove from heat. Let stand, covered, for 5 minutes. Stir in Parmesan cheese.
