Cook spaghetti pasta according to package instructions until al dente. Drain and set aside.
In a large skillet over medium heat, sauté diced onion, green bell pepper, and minced garlic until softened, about 5 minutes.
Add ground beef to the skillet and cook until browned, breaking it up into crumbles with a spoon.
Stir in diced tomatoes, tomato sauce, chili powder, cumin, salt, and black pepper.
Simmer the sauce for 15 minutes, allowing the flavors to meld and the sauce to thicken.
Serve the spaghetti twirled into mounds on plates, topped generously with the chunky meat sauce.
Sprinkle shredded cheddar cheese over each serving while still hot, allowing it to melt slightly.