Step 1: Season and Sear the Chicken
Pat the chicken breasts completely dry with paper towels. This is crucial for a good sear. Rub the Cajun seasoning all over the chicken, coating it thoroughly. Heat the olive oil in a large, deep skillet or braiser over medium-high heat. Once the oil is shimmering, add the chicken. Cook for 5-7 minutes per side, until deeply golden brown and cooked through (internal temp of 165°F). Transfer the chicken to a clean plate, cover loosely with foil, and let it rest.

Step 2: Build the Flavor Foundation
Without cleaning the skillet, reduce the heat to medium. Add the 3 tablespoons of butter. Once melted, add the minced garlic and sauté for about 30 seconds to 1 minute, until fragrant. Be careful not to burn it.

Step 3: Deglaze and Start the Sauce
Pour in the chicken broth to deglaze the pan. Use a wooden spoon to scrape up all the browned bits (the fond) from the bottom of the skillet—this is pure flavor. Bring the broth to a simmer.

Step 4: Cook the Pasta in the Sauce
Break the fettuccine in half and add it directly to the simmering broth in the skillet. Ensure the pasta is mostly submerged. Pour in the heavy cream. Stir gently, bring the liquid back to a steady simmer, then reduce the heat to medium-low. Cover the skillet and let the pasta cook for 12-15 minutes, stirring occasionally, until the pasta is al dente and has absorbed much of the liquid. The sauce will thicken as it cooks.

Step 5: Create the Creamy Alfredo
Once the pasta is tender, reduce the heat to low. Gradually sprinkle in the 1 cup of grated Parmesan cheese, stirring constantly until it is fully melted and the sauce is smooth. Stir in the smoked paprika and lemon juice. Taste the sauce and adjust seasoning with salt and pepper—be cautious, as the Cajun chicken and Parmesan are already salty.

Step 6: Slice and Incorporate the Chicken
Slice the rested Cajun chicken into ½-inch thick strips or bite-sized pieces. Nestle the sliced chicken back into the skillet with the creamy pasta, along with any accumulated juices from the plate. Gently toss everything together to coat the chicken in the sauce and reheat it slightly.

Step 7: Garnish and Serve Immediately
Remove the skillet from the heat. Garnish generously with fresh parsley and sliced green onions. Serve directly from the skillet, offering extra Parmesan cheese, lemon wedges, and red pepper flakes on the side for individual customization.