In a medium saucepan, melt the butter over medium heat.

Add the diced onion to the melted butter and sauté until softened.

Stir in the long grain white rice, along with garlic powder and salt, and cook for an additional minute.

Pour in the chicken stock and milk, then bring the mixture to a gentle boil.

Reduce the heat to low and let the rice simmer, covered, for about 20 minutes.

Remove from heat and stir in reserved milk, lemon juice, lemon zest, and Parmesan cheese.

Adjust salt if necessary, garnish with parsley, and serve hot.