Heat the oven to 375°F. Lightly grease a 12-cup muffin tin. Rinse the rice under cold water and set it aside to drain.

Heat the olive oil in a medium saucepan over medium heat. Add half of the onion, bell pepper, and celery. Cook for 4 to 5 minutes, stirring occasionally, until softened.

Add the rinsed rice, smoked paprika, cayenne, 1 teaspoon of the Cajun seasoning, and 1/4 teaspoon of the salt. Stir to coat the rice, then add 1 cup of the beef broth. Bring to a boil, cover, and reduce the heat to low. Cook according to the rice package directions, until tender and the liquid is absorbed.

While the rice cooks, put the remaining ground beef in a large mixing bowl. Add the egg, breadcrumbs, tomato paste, remaining onion, bell pepper, and celery, 1 teaspoon Cajun seasoning, the remaining 1/4 teaspoon salt, and the black pepper. Mix gently until combined.

Divide the beef mixture among 8 muffin cups, pressing it in lightly. Bake for 20 to 25 minutes, until the centers reach 160°F.

When the rice is cooked, fluff it with a fork. Stir in the remaining 1/2 cup beef broth and half of the parsley. Simmer uncovered for 2 to 3 minutes, stirring gently, until the rice is moist but not soupy.

Let the meatloaf muffins rest in the pan for 5 minutes. Serve them with the dirty rice and sprinkle the remaining parsley over the rice.