Step 1

Preheat oven to 350 degrees F (175 degrees C).

Step 2

Place butter into a 9x13-inch baking dish and set in oven while it preheats until butter is melted, about 5 minutes.

Step 3

Stir onion, basil, red pepper flakes, salt, and black pepper into melted butter. Add chicken, turning to coat with onion mixture and ending skin-side up.

Step 4

Bake in the preheated oven until no longer pink at the bone and the juices run clear, about 1 hour. An instant-read thermometer inserted near the bone should read 165 degrees F (74 degrees C). Remove chicken from dish.

Step 5

Bring a large pot of lightly salted water to a boil. Cook linguine at a boil until tender yet firm to the bite, about 11 minutes; drain.

Step 6

Mix spinach into onion-butter sauce until thoroughly mixed; add linguine and Parmesan cheese, tossing to combine. Place chicken on top of pasta.