Bring saltwater to a boil (4 quarts water + 1 tbsp salt) in a large pot. Add bowtie pasta, cook according to package instructions for al dente. Reserve 1/2 cup pasta water before draining.
In a small bowl, combine Cajun seasoning: paprika, garlic powder, onion powder, cayenne, salt, pepper, oregano, and thyme. Set 1 tbsp aside for sautéing veggies.
In a mixing bowl, toss shrimp with 2 tbsp olive oil and 3 tbsp cajun seasoning. Let marinate 5-10 minutes for best flavor.
Heat 2 tbsp butter in a Dutch oven or skillet over medium-high. Cook shrimp in single layer (in batches if needed) 1-2 minutes per side until ‘C’ shape forms. Remove to plate.
Reheat pan, add 2 tbsp butter and 1 tbsp reserved cajun seasoning. Cook onions and bell peppers 4 minutes, then add garlic and cook 1 minute. Stir constantly to avoid burning.
Pour in heavy cream, bring to gentle boil. Reduce heat to medium, simmer 2-3 minutes. Add parsley and cooked shrimp.
Return cooked pasta to pan, stir to coat. Add remaining 1/2 cup pasta water as needed to loosen sauce. Serve with extra parsley.