Season the shrimp: Pat the shrimp dry with paper towels. Toss with 1 to 2 teaspoons of the Cajun seasoning and a pinch of salt.
Set aside while you start the rice.
Sauté the aromatics: Heat 1 tablespoon olive oil in a large skillet over medium heat. Add onion and bell peppers. Cook 4 to 5 minutes until softened, stirring occasionally.
Add garlic and spices: Stir in garlic, remaining Cajun seasoning, smoked paprika, and cayenne (if using).
Cook 30 seconds until fragrant. If using tomato paste, stir it in now and cook another 30 seconds.
Toast the rice: Add the uncooked rice. Stir to coat in the spices and oil, toasting for 1 minute.
This helps keep the grains fluffy.
Simmer: Pour in the broth. Season with salt and black pepper. Bring to a gentle boil, then reduce to a low simmer.
Cover and cook 13 to 15 minutes, or until the rice is tender and most liquid is absorbed.
Cook the shrimp: When the rice is nearly done, nestle the seasoned shrimp on top in a single layer. Cover and cook 3 to 4 minutes, until the shrimp are pink and opaque. Avoid overcooking.
Finish and fluff: Remove from heat.
Squeeze in lemon juice and sprinkle parsley. Fluff gently with a fork to mix the shrimp and rice without smashing the grains.
Taste and adjust: Add more salt, a dash of Cajun seasoning, or a splash of broth if you want it a bit saucier. Serve hot.