Bring a large pot of salted water to a boil. Cook fettuccine according to package directions until al dente. Drain and set aside.

While the pasta cooks, place the chopped bacon in a large, deep skillet over medium heat. Cook until brown and crispy, about 8-10 minutes. Use a slotted spoon to remove the bacon to a paper towel-lined plate, leaving about 2 tablespoons of bacon fat in the skillet.

Season the chicken pieces with salt and pepper. Add the chicken to the skillet with the bacon fat and cook over medium-high heat until golden brown and cooked through, about 5-7 minutes. Remove the chicken and set aside.

Reduce heat to medium. Add the butter to the skillet. Once melted, add the minced garlic and cook for 30-60 seconds until fragrant. Whisk in the flour and cook for 1 minute, stirring constantly.

Slowly whisk in the chicken broth, scraping up any browned bits from the bottom of the pan. Once smooth, slowly pour in the heavy cream and the ranch seasoning packet. Bring to a gentle simmer and cook for 3-4 minutes, stirring, until it begins to thicken.

Reduce the heat to low. Gradually stir in the shredded cheddar and grated Parmesan cheese until completely melted and the sauce is smooth. Do not let it boil. Taste and adjust seasoning with salt and pepper if needed.

Add the cooked pasta, cooked chicken, and half of the crispy bacon to the sauce. Toss gently to coat everything evenly. Let it simmer for 1-2 minutes for the flavors to meld.

Serve immediately, garnished with the remaining crispy bacon and fresh parsley or chives.