Brown the ground beef in a large skillet over medium heat, breaking it up as it cooks.
Drain any excess fat. Stir in the onion and cook until softened, about 3 minutes.
Add the garlic and cook until fragrant, about 30 seconds.
Lower the heat. Stir in the tomatoes with chilies and the cheese cubes.
Cook gently, stirring often, until the cheese melts and the dip is smooth, 5–7 minutes.
Season with chili powder and cumin. Splash in milk to reach your preferred consistency.
Sprinkle with cilantro and green onion. Keep warm on low heat or in a slow cooker on Warm.