1. Combine milk and broth in a medium saucepan over high heat. Heat until mixture starts to boil.
2. Stir in oats and reduce heat to a simmer. Cook for 25 to 30 minutes, stirring occasionally, until liquid is absorbed. Oats should be tender and cooked through.
3. Stir in cheese and green onion. Top with tomatoes.
4. Refrigerate leftovers within 2 hours.