Heat the olive oil in a large skillet over medium-high heat. Cook the chicken until it's golden brown and cooked through, about 6-8 minutes per side. Once done, transfer it to a plate and cover with foil to keep warm.

Lower the heat to medium in the same skillet and add the butter. Let it melt, then add the minced garlic. Stir and cook until fragrant, about 1-2 minutes.

Pour in the heavy cream, half and half, buffalo sauce, Italian seasoning, and a pinch of pepper. Mix everything well and let it come to a gentle simmer.

Stir in 1/2 cup of the grated parmesan cheese into the skillet. Whisk until the cheese melts and the sauce thickens slightly, around 3-5 minutes.

While the sauce simmers, bring a pot of salted water to a boil and cook the fettuccini according to package instructions until al dente, typically around 8-10 minutes.

Use a slotted spoon to transfer the cooked fettuccini directly to the skillet with the sauce.

Pour in 1/3 cup of the starchy pasta water to the skillet, helping the sauce adhere to the fettuccini. Toss everything gently to combine.

Mix in the diced chicken and sprinkle the remaining 1/4 cup of parmesan cheese on top. Give it a final toss and garnish with minced parsley before serving.