In a large skillet or Dutch oven, cook the chopped bacon over medium heat until crispy. Remove the bacon with a slotted spoon and set aside on paper towels to drain. Leave the bacon grease in the pan.

Increase the heat to medium-high. Add the ground beef to the skillet with the bacon grease. Cook, breaking it apart with a spoon, until browned and no longer pink. Drain excess fat if necessary.

Reduce the heat to medium. Add the diced onion, minced garlic, and diced green bell pepper (if using) to the skillet. Sauté until the vegetables are soft and fragrant, about 5 minutes.

Stir in the diced tomatoes (with juice), tomato sauce, barbecue sauce, Worcestershire sauce, and red pepper flakes. Season with salt and pepper to taste. Bring the mixture to a simmer.

Add the cooked spaghetti to the sauce, tossing to combine. Let it simmer for a few more minutes so the spaghetti absorbs some of the sauce flavors.

Stir in the cooked bacon. Sprinkle the shredded cheddar cheese over the top of the spaghetti and cover the skillet with a lid. Let it sit on low heat until the cheese is melted, about 3-5 minutes.

Serve the Cowboy Spaghetti hot, garnished with sliced green onions on top.