Cook the beef: Heat some oil in a large Dutch oven over medium-high heat. Add the ground beef, season with salt and pepper, and add the cayenne, cumin, and garlic powder. Sauté until fully cooked, then remove to a separate bowl along with any and all juices.
Cook the rice: Boil 2 cups of water in a small saucepan. Rinse the rice well and add it to the boiling water along with the bay leaves. Cover, reduce the heat to low, and simmer for 20 minutes while you proceed with the recipe.
Make the roux: Add the vegetable oil to the same Dutch oven as before (don't clean it out). Heat until very hot and smoking slightly, turn the heat down a bit, add the flour, and begin to stir with a wooden spoon. Stir constantly until the roux darkens to the color of milk chocolate, anywhere between 5 and 15 minutes.
Cook the vegetables: Once the roux is dark enough, add the vegetables (onion, carrot, celery, and green bell pepper) to the Dutch oven and stir to coat with the roux. Sauté until the vegetables are soft and glistening, about 10 minutes. Add ⅓ cup water, the cornstarch, and any juices from the beef, stirring until the mixture has thickened and resembles gravy.
Assemble: Remove the bay leaves from the rice. Stir together the ground beef, vegetable mixture, bacon bits, rice, and salted butter. Taste for salt, adding more if needed. Garnish with chopped scallions and serve hot.