Bring a large pot of salted water to a boil and cook the spaghetti according to package directions; drain and set aside.
In a large skillet over medium heat, brown the ground hamburger, breaking it up with a spoon as it cooks.
When the beef is mostly browned, drain excess grease. Add the diced onion, minced garlic, and garlic powder to the skillet; stir and cook about 4–5 minutes until the onion is softened.
Add the diced fire roasted tomatoes, rinsed pinto beans, drained corn, the Campbell's Mexican Style Tomato soup, and 1/2 cup salsa to the beef mixture; stir to combine and bring to a simmer.
Toss the simmering beef mixture with the drained spaghetti until well combined and heated through.
Portion the spaghetti into ovenproof bowls or a broiler-safe baking dish, top with avocado chunks, chopped green onion, and a generous sprinkling of shredded cheddar.
Place under a hot broiler about 1 minute, watching closely, just until the cheese melts; remove and serve immediately.