Season the cubed chicken generously with salt and pepper.
Heat the olive oil in a 6-quart Dutch oven or medium pot over medium-high heat.
Add the seasoned chicken and brown on all sides, about 3–4 minutes, without cooking through; remove any excess liquid if necessary.
Add the minced garlic to the pot and sauté for about 30 seconds until fragrant.
Pour in the chicken broth and heavy cream, then add the fettuccine and the basil sprig.
Bring the mixture to a boil, then reduce heat to a simmer.
Simmer, stirring occasionally, for 15–20 minutes until the pasta is tender and most liquid is absorbed.
Stir in the frozen peas and cook 1 minute more until heated through.
Remove the basil sprig, stir in the grated Parmesan until melted and combined, and adjust seasoning with salt and pepper if needed.
Serve immediately.
