Steam onions in the microwave. Place in a microwave-safe bowl, cover loosely with microwave-safe plastic wrap and microwave on high for 2 minutes.
Stir in garlic, drained tomatoes, milk, chopped chiles, cumin, oregano and pepper.
Tear cheese slices.
Place torn cheese into slow cooker.
Pour onion mixture over cheese.
Cover, and cook on low for 2 hours. Stir gently to blend ingredients.
As with any of my recipes, calorie counts and nutritional information varies greatly depending on which products you choose to use when cooking this dish.