In a large skillet over medium-high heat, heat oil. Add onion and cook 3 minutes until softened. Stir in garlic for 30 seconds, then add chicken, taco seasoning, salt, and pepper. Cook 6–8 minutes, stirring occasionally, until chicken is no longer pink.

Reduce heat to low. Add the can of tomatoes with green chiles and cream cheese, stirring until cream cheese melts, about 2 minutes. Stir in shredded cheese and milk, and cook 2–3 minutes until smooth and creamy. Add more milk if needed.

Warm tortillas by charring them over a gas burner, heating in a dry skillet for 30 seconds per side, or microwaving them in a damp paper towel for 30 seconds.

Spoon queso chicken onto each tortilla, add your favorite toppings, and serve right away.