Pat shrimp dry and toss with 2 tablespoons Cajun seasoning and 1 tablespoon oil.
Sear shrimp in a hot skillet for 2 minutes per side. Remove and set aside.
Add oil and onions to the skillet. Cook 3–4 minutes until soft.
Stir in garlic, remaining seasoning, and rice. Toast for 1 minute.
Pour in broth, diced tomatoes, and tomato paste. Stir and bring to a boil.
Reduce heat, cover, and simmer for 20 minutes.
Turn off heat, return shrimp to the pan, and cover for 1–2 minutes.
Garnish with lemon and parsley before serving.