Season chicken with ½ teaspoon salt and ¼ teaspoon pepper; heat oil in a large deep skillet or pot over medium-high.
Cook chicken 5-6 minutes until golden and cooked through; set aside on a plate.
Melt butter in same pot over medium; sauté garlic 1 minute until fragrant.
Add broth, cream, remaining salt and pepper, garlic powder, and optional nutmeg; stir and boil.
Submerge broken fettuccine; reduce heat to medium and cook 10-12 minutes, stirring frequently to prevent sticking, until tender.
Return chicken; stir and remove from heat.
Stir in Parmesan until melted and creamy; stand 2-3 minutes to thicken.
Garnish with fresh parsley and optional extra Parmesan; serve immediately while hot and creamy.