Bring a large pot of generously salted water to a boil and cook the spaghetti until al dente according to package directions; drain, toss with a little olive oil, and set aside.
Heat 1 tablespoon olive oil in a large Dutch oven or deep skillet over medium-high heat. Add the diced onion and sauté about 5 minutes until softened.
Add the ground meat and cook, breaking it up with a spoon, until browned and cooked through and the onions are tender.
Stir in the tomato paste, minced garlic, chili powder, ground cumin, salt, dried oregano, smoked paprika, black pepper, and cayenne (if using). Cook 1 minute to bloom the spices.
Pour in 1 cup water and scrape the bottom of the pan to deglaze. Add the fire-roasted diced tomatoes (with liquid), canned diced green chiles, and beef bouillon; stir to combine.
Simmer uncovered for about 5 minutes, stirring occasionally, until flavors meld and the sauce thickens slightly.
Remove the pan from heat and stir in the shredded cheddar and grated Monterey Jack a handful at a time until fully melted and incorporated into the sauce.
Add the cooked spaghetti to the sauce and toss until evenly coated; adjust seasoning with additional salt, pepper, or cayenne to taste.
Serve topped with crushed tortilla chips, extra cheese, diced tomatoes, diced avocado, chopped cilantro, and a dollop of sour cream as desired.
