Bring a large pot of salted water to a boil and cook the spaghetti according to package directions for al dente; drain and set aside.
While the pasta cooks, heat a large skillet over medium heat and add the ground hamburger; cook, breaking it up with a spoon, until browned.
Drain excess grease from the skillet, then add the diced yellow onion, minced garlic, and garlic powder; stir and cook about 5 minutes until the onion is softened.
Stir in the diced fire-roasted tomatoes, rinsed pinto beans, drained corn, the Mexican-style tomato soup, and 1/2 cup salsa; bring to a simmer.
Add the cooked, drained spaghetti to the skillet (or pour the meat mixture over the pasta) and toss gently until well combined and heated through.
Portion the spaghetti into broiler-safe bowls or a baking dish, top with avocado chunks, chopped green onion, and shredded cheese.
Place under a hot broiler for about 1 minute, just until the cheese melts, then remove and serve immediately.
