Add the meatballs to the bowl of your slow cooker.
1 32 oz pkg frozen meatballs
Heat the oil in a large skillet set over medium high heat. Once the oil's hot add the onions, stirring to combine. Saute until softened, stirring occasionally, until tender.
1 tbsp extra virgin olive oil, 1 small yellow onion
Add the garlic and saute for 60 seconds.
1 1/2 tbsp minced garlic
Add the beer, tomato paste, barbecue sauce, sugar, Worcestershire, mustard, and thyme to the skillet then whisk together until everything's evenly combined.
1 1/2 cups Guinness beer, 1 8 oz can tomato paste, 1/2 cup barbecue sauce, 1/2 cup brown sugar, 1 tbsp Worcestershire sauce, 1 tbsp Dijon mustard, 1 tsp dried thyme leaves
Bring the sauce to a boil then immediately reduce the heat to low and simmer for 8-10 minutes, stirring often.
Pour the sauce evenly out overtop of the meatballs, then give everything a stir to evenly coat.
Cover and cook on LOW for 2-3 hours.
Serve plain, with a side of steamed rice, or over mashed potatoes.