Step 1: Preheat oven to 375°F (190°C). Bring a large pot of salted water to a rolling boil. Add pasta and cook according to package directions until al dente. Drain and set aside.
Step 2: Pat chicken thighs dry with paper towels. Season with 1/2 teaspoon salt, 1/4 teaspoon black pepper, and garlic powder. Heat 1 tablespoon olive oil in a large oven-safe skillet or Dutch oven over medium-high heat. Sear chicken for 3-4 minutes per side until golden brown. Remove chicken from skillet and set aside.
Step 3: In the same skillet, add the remaining 1 tablespoon olive oil (if needed) and minced garlic. Sauté for 1 minute until fragrant. Pour in chicken broth and heavy cream, scraping up any browned bits. Bring to a gentle simmer.
Step 4: Reduce heat to low, add Boursin cheese, and whisk continuously until melted and smooth. Stir in red pepper flakes (if using) and Italian herbs. Season with remaining 1/2 teaspoon salt and 1/4 teaspoon black pepper, or to taste.
Step 5: Add the cooked al dente pasta to the skillet and toss to coat with the Boursin sauce. Nest the seared chicken thighs into the pasta mixture. Sprinkle with mozzarella and Parmesan cheeses.
Step 6: Bake for 20-25 minutes, or until chicken is cooked through (internal temperature 165°F/74°C), sauce is bubbly, and cheese is golden. For extra browning, broil for the last 2-3 minutes, watching closely.
Step 7: Remove from oven, let rest for a few minutes, then garnish with fresh parsley or basil before serving.