Place roast in a slow cooker.
Sprinkle with dressing mix; pour beer over top.
Add onion and peppers.
Cook on high setting for 5 to 6 hours, until meet easily shreds with a fork.
Brush buns with butter and sprinkle with garlic butter.
Toast at 350 for 10-12 minutes until lightly brown.
Place a slice of cheese on hot bread and spoon mixture onto sandwich buns