Heat the vegetable oil in a large pot or Dutch oven over medium-high heat. Add the ground beef and the chopped onion and garlic. Sauté for a few minutes until they become fragrant and slightly softened.
Add the carrots, celery, and green bell pepper to the pot. Cook for another 5 minutes, stirring occasionally, until the vegetables start to soften.
Add the diced tomatoes (with their juices) and beef broth. Stir well to combine.
Add the drained kidney beans, corn kernels, and spices to the pot. Stir to distribute the spices evenly.
Remember that the beef broth might already contain some salt, so adjust accordingly.
Bring the soup to a boil, then reduce the heat to low. Cover the pot and let it simmer for about 1 hour, or until the beef is tender and the flavors have melded together.
Taste and adjust the seasonings if needed. If you prefer a thicker soup, you can use a spoon to mash some of the beans against the side of the pot to thicken the broth.
Serve the cowboy soup hot, garnished with chopped fresh parsley if desired. It pairs well with crusty bread or cornbread.