Heat a large skillet over medium-high heat. Add the ground beef and diced onion. Cook for 6–8 minutes, breaking up the meat, until the beef is browned and the onion is soft. Drain excess grease if needed.
Reduce heat to medium. Sprinkle in the flour, chili powder, garlic powder, cumin, and oregano. Stir well and cook for 1 minute, until fragrant. Stir in the tomato paste until evenly combined.
Slowly pour in the broth while stirring continuously to prevent lumps. Bring to a gentle simmer and cook for 7–10 minutes, until the sauce thickens slightly. Taste and add salt if needed.
While the sauce simmers, cut the tortillas into thin strips. I like to cut them in half, then into 8 pieces.
Stir the tortilla strips into the sauce until evenly coated.
Sprinkle cheese evenly over the top. Remove from heat, cover, and let sit for 3–5 minutes to allow the cheese to melt and the tortillas to soften slightly.
Top with sour cream and fresh cilantro. Serve immediately.