Heat the olive oil in a large skillet over medium-high heat. Season the pork with salt and pepper, then sear it in the skillet until browned on all sides, about 3-4 minutes per side. Transfer the pork to the crockpot.

In the same skillet, add the diced onion and garlic. Sauté for 2-3 minutes until the onion is translucent. Add the chicken broth, barbecue sauce, apple cider vinegar, smoked paprika, ground cumin, and chili powder. Stir to combine and bring to a simmer.

Pour the sauce mixture over the pork in the crockpot. Cover and cook on low for 8 hours or on high for 4 hours, until the pork is tender and easily shredded with a fork.

Once cooked, remove the pork from the crockpot and shred it with two forks. Return the shredded pork to the crockpot and stir to combine with the sauce.

To assemble the bowls, divide the cooked rice or quinoa among serving bowls. Top with the pulled pork, corn, black beans, diced tomatoes, and avocado slices. Garnish with fresh cilantro if desired.