Warm olive oil in a medium skillet over medium heat. Add the ground beef and diced onion to the pan. Cook, breaking up the beef with a spoon as you go, for 6 to 8 minutes until browned.
In the meantime, prep the vegetables by dicing them into very small pieces. This is an important step, because finely dicing the veggies makes them easier to cook in the slow cooker and more palatable to eat in the dish.
Add the cooked beef and onion to the slow cooker. If desired, drain the grease from it before adding it. You can also use a slotted spoon to remove it from the skillet so that excess grease drips off of it.
Add the carrots, bell pepper, celery, tomato paste, onion powder, garlic powder, chili powder, salt, smoked paprika, and black pepper. Pour in 3 cups of the beef broth (save the last cup for later).
Cover the slow cooker and cook on high for 3 to 4 hours or low for 6 to 8 hours until the vegetables are softened. Cooking times may vary depending on the slow cooker. Check as early as 2 and a half hours if you have a newer model that you know cooks things quickly.
Add the macaroni and last cup of broth to the slow cooker. Stir well, cover, and cook for 15 more minutes until the macaroni is tender. Stir occasionally to promote even cooking.
Add the milk, cheese, and parsley to the slow cooker. Keep stirring until the cheese melts and the macaroni is creamy.
Serve immediately and enjoy!
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