Prepare slow cooker pork first: Season the pork generously all over with salt, pepper and cumin and place it in the slow cooker.
Place onions and bell peppers on top of the pork and sprinkle with salt and pepper.
Cover and cook on low in slow cooker for 8 hours.
When pork is done cooking, remove to a cutting board and shred with two forks. Place pork in a bowl with the onions and bell pepper and some of the liquid left in the slow cooker.
Make your tacos: Assemble all of your ingredients for the tacos on the kitchen counter. Place one tortilla on a plate, add pulled pork and any additional toppings you would like.