Preheat oven to 400°F (200°C) or air fryer to 375°F (190°C). In a bowl, toss halved brussels sprouts with 2 tbsp olive oil, minced garlic, 1/4 tsp salt, and 1/8 tsp black pepper.

If baking: Spread brussels sprouts in a single layer on a baking sheet. Roast for 20-25 minutes, flipping halfway, until tender and lightly charred.

If air frying: Place brussels sprouts in a single layer in the air fryer basket (cook in batches if necessary). Air fry for 12-15 minutes, shaking the basket halfway, until tender and crispy. Set aside.

While brussels sprouts cook, pat chicken cubes dry. In a medium bowl, toss chicken with 1 tbsp olive oil, 1/2 tsp salt, 1/4 tsp black pepper, 1/2 tsp garlic powder, and 1/4 tsp Italian seasoning.

Heat a large skillet over medium-high heat. Add seasoned chicken and cook for 5-7 minutes, stirring occasionally, until browned and cooked through. Remove chicken from the skillet and set aside.

Bring a large pot of salted water (8 cups water, 1 tsp salt) to a rolling boil. Add fettuccine and cook according to package directions until al dente.

Before draining, reserve 1/4 cup of pasta water. Drain the pasta and set aside.

In the same large skillet (no need to clean it after chicken), melt 4 tbsp unsalted butter over medium heat. Add 2 cloves minced garlic and sauté for 1 minute until fragrant.

Slowly whisk in the heavy cream. Bring to a gentle simmer, then reduce heat to low.

Gradually whisk in the grated Parmesan cheese until the sauce is smooth and thickened. Season with 1/4 tsp salt, 1/8 tsp black pepper, and a pinch of nutmeg if desired. If the sauce is too thick, add a tablespoon or two of reserved pasta water until desired consistency is reached.

Add the cooked pasta and cooked chicken to the Alfredo sauce in the skillet. Toss gently to coat everything evenly.

Divide the chicken alfredo among serving plates. Top each serving with the roasted garlic brussels sprouts. Drizzle with balsamic glaze if using, and garnish with extra Parmesan cheese and fresh parsley, if desired.