Add the cavatappi pasta and 2 cups of water to the slow cooker insert. Cover and cook on low for 30 minutes, stirring once halfway through, until the pasta is just tender but still firm.

While the pasta cooks, melt the butter in a small saucepan over medium heat. Add the minced garlic and red pepper flakes, cooking for 30 seconds until fragrant but not browned. Remove from heat.

Drain the pasta well and return it to the slow cooker. Stir in the heavy cream, chicken broth, lemon juice, and half of the Parmesan cheese. Stir in the butter mixture and toss gently until everything is coated and the sauce is creamy.

Sprinkle the remaining Parmesan cheese over the top. Sear the shrimp in a quick pan with olive oil for 1-2 minutes per side until pink, then scatter over the pasta. Top with chopped parsley and serve immediately.