Bring a pot of water to a boil and season generously with salt. Cook the fettuccine for 1 minute less than the packet instructions. Drain and reserve ½ - 1 cup of pasta water.
Slice the chicken into two fillets and place them in a bowl. Add the onion and garlic powder, smoked paprika, salt, and pepper. Mix well.
Place a pan over medium-high heat and add olive oil. Sear the chicken for 2 ½ - 3 minutes on each side or until cooked in the centre. Remove, rest for 5 minutes, and thinly slice.
Place the same pan or a clean pan over medium heat. Add the butter and garlic, and sauté for 2 minutes or until the butter starts to foam and the garlic is fragrant but not brown.
Increase the heat to medium-high, add cream and mix well. Season to taste and bring to a boil. Reduce heat to low and simmer for 5-6 minutes or until thick and slightly reduced. Add Parmigiano Reggiano and nutmeg and gently mix to combine.
Add the drained pasta, mix to coat and cook for 1 minute. Adjust with the reserved pasta water if required. Remove from heat.
Serve the creamy Alfredo pasta in a bowl, laying the sliced chicken on top. Garnish with flat-leaf parsley and Parmigiano Reggiano. Dig in.