Heat olive oil in a large pot over medium-high heat.
Add diced onion and cook for 2 minutes until softened.
Add minced garlic and cook for 30 seconds until fragrant.
Add ground beef to the pot and cook, breaking it apart with a spoon, until browned and no longer pink, about 5-7 minutes.
Drain excess fat from the pot if necessary.
Add diced red bell pepper and sliced mushrooms to the pot and cook for 3 minutes until slightly softened.
Stir in the diced tomatoes with their juice, beef broth, dried Italian seasoning, salt, and black pepper.
Bring the mixture to a boil.
Add the uncooked penne pasta and stir to combine.
Reduce heat to medium-low, cover the pot, and simmer for 12-15 minutes, stirring occasionally, until the pasta is cooked and most of the liquid is absorbed.
Remove the pot from heat and sprinkle shredded cheddar cheese over the top.
Cover the pot again and let it sit for 2 minutes to allow the cheese to melt.
Stir gently to combine the melted cheese into the pasta and serve immediately.