Heat a large, deep skillet (at least 12-inch) over medium-high heat. Add ground beef and diced onion. Cook, breaking up the beef with a wooden spoon, until the beef is browned and the onion is softened, about 8-10 minutes. Drain any excess grease from the skillet.

Add minced garlic and taco seasoning to the skillet. Cook for 1 minute more, stirring constantly, until fragrant. Stir well to ensure all ingredients are combined and scrape up any browned bits from the bottom of the pan.

Pour in the undrained diced tomatoes with green chilies, tomato sauce, and chicken broth. Bring the mixture to a gentle simmer, stirring occasionally.

Break the spaghetti in half and add it to the simmering sauce, fanning it out to ensure it's mostly submerged. Stir gently to incorporate the pasta into the sauce. Reduce heat to medium-low, cover the skillet with a lid, and cook for 15-20 minutes, stirring occasionally (every 5 minutes or so) to prevent sticking and ensure even cooking, until the spaghetti is al dente and most of the liquid has been absorbed.

Remove the skillet from heat. Stir in the sour cream and 1 cup of shredded sharp cheddar cheese until melted, smooth, and creamy. Taste and adjust seasoning if needed.

While the spaghetti cooks, preheat your oven to 375°F (190°C). Stack the corn tortillas and slice them into thin strips or small triangles. In a medium bowl, toss the tortilla pieces with olive oil until lightly coated. Spread them in a single layer on a baking sheet.

Bake for 8-12 minutes, flipping halfway through, until the tortilla pieces are golden brown and crispy. (Alternatively, you can air fry at 375°F/190°C for 4-7 minutes, shaking the basket halfway).

Once crispy, remove the baking sheet from the oven. Immediately sprinkle the 1/2 cup shredded Monterey Jack or Mexican blend cheese over the hot tortilla strips. Return to the oven for 2-3 minutes, or until the cheese is melted and bubbly. Watch carefully to prevent burning.

Ladle the hot taco spaghetti into individual bowls. Top each serving generously with the cheesy tortilla crunch and an extra sprinkle of fresh shredded cheddar or a dollop of sour cream, if desired. Serve immediately.