Preheat the oven to 350 degrees F. In a large bowl, combine the ground beef, breadcrumbs, milk, half the diced onion, half the diced bell pepper, 2 minced garlic cloves, 2 tablespoons Cajun seasoning, and salt. Mix until evenly combined, then shape into a loaf.
Place the meatloaf into a loaf pan and bake for 50 minutes, or until the center reaches 160 degrees F.
While the meatloaf bakes, heat a skillet over medium heat. Add the remaining onion and bell pepper and cook for 3 minutes until softened. Stir in the remaining garlic clove, 1 tablespoon Cajun seasoning, rice, red beans, and chicken broth.
Bring the mixture to a simmer, cover the skillet, and cook for 20 minutes until the rice is tender and the liquid is absorbed.
Remove the meatloaf from the oven and let it rest for 5 minutes. Slice and serve alongside the red beans and rice. Sprinkle chopped green onions over the top before eating.