Cook the spaghetti in generously salted boiling water according to package directions until al dente, drain, toss with a little olive oil, and set aside.
Heat 1 tablespoon olive oil in a large Dutch oven or heavy skillet over medium-high heat; add the diced onion and sauté about 5 minutes until softened.
Add the ground beef (or turkey or chicken) 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, and pepper; cook 1 minute until fragrant.
Pour in 1 cup water and scrape the bottom of the pan to deglaze, then add the fire-roasted diced tomatoes (with liquid), diced green chiles, and beef bouillon; stir to combine.
Simmer uncovered for about 5 minutes, stirring occasionally, until flavors meld and sauce slightly thickens.
Remove the pan from heat and stir in the shredded cheddar and Monterey Jack a handful at a time until melted and sauce is creamy.
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, avocado, chopped cilantro, and a dollop of sour cream as desired.