Heat olive oil in a large skillet or Dutch oven over medium-high heat until shimmering. Make sure to use a pan with high sides and a lid, as this is truly a one-pot recipe.
Add ground beef and diced onion to the hot pan. Break the beef apart with a wooden spoon and season with a pinch of salt and pepper. Cook until the beef is no longer pink and the onions are softened, about 5-7 minutes.
Add the minced garlic, Italian seasoning, smoked paprika, and red pepper flakes (if using). Stir and cook for about 30 seconds until fragrant. Your kitchen should smell amazing right about now!
Stir in the tomato paste and cook for 1-2 minutes, allowing it to caramelize slightly. This develops a deeper, richer flavor.
Pour in the diced tomatoes with their juice and the tomato sauce. Stir well, scraping up any browned bits from the bottom of the pan – that's flavor gold!
Add the beef broth and bring the mixture to a boil. Once boiling, add any optional vegetables you're using.
Stir in the uncooked macaroni, making sure it's all submerged in the liquid. Reduce heat to medium-low, cover, and simmer for about 10-12 minutes, stirring occasionally to prevent sticking, until the pasta is tender and most of the liquid has been absorbed.
Once the pasta is cooked to al dente, remove the pan from heat. If it seems too soupy, let it stand uncovered for a few minutes to thicken. If it's too thick, add a splash more broth.
Add the shredded cheese and stir until it's melty and well incorporated throughout the dish. The residual heat will melt the cheese perfectly without making it stringy.
Taste and adjust seasoning with additional salt and pepper if needed.
Sprinkle with grated Parmesan cheese and chopped parsley before serving. Dig in and watch it disappear!