Heat 2 tbsp olive oil in a skillet over medium-high heat. Add shrimp and Cajun seasoning. Cook about 30 seconds per side, then remove and set aside.
Add remaining olive oil, 2 tbsp butter, garlic, and red pepper to the skillet. Cook about 20 seconds until fragrant.
Stir in chicken stock (or white wine), lemon juice, and capers. Reduce heat to medium-low and simmer 10–15 minutes until slightly reduced.
Meanwhile, cook pasta according to package instructions. Reserve 1/2 cup pasta water, then drain.
Stir pasta water into the sauce and cook 1 minute. Add remaining butter and stir until melted.
Add pasta and shrimp back into the skillet. Toss until fully coated.
Garnish with parmesan and parsley before serving.