Spray your slow cooker with non-stick cooking spray. Season pork with salt and pepper and place in the slow cooker. Sprinkle chili powder, cumin, oregano and cinnamon over the pork. Place onions, garlic and tomatoes around the pork and pour chicken broth on top. Cover and cook on HIGH for 4-5 hours or LOW for about 8 hours. Shred the pork.
For the Salsa: Add everything but the pineapple to a bowl. Heat your grill or grill pan to medium-high. Brush pineapple slices with a little bit of olive oil and place on the hot grill, cooking for about 2 minutes on each side. Chop the pineapple and add it to the bowl with the remaining ingredients. Stir to combine.
Add avocado flesh to a small bowl and mash with a fork. Add a tiny bit of lemon juice and season with a little salt. Stir to combine.
Top each tortilla with shredded pork, a spoonful of guacamole, and a spoonful of grilled pineapple salsa.
Notes
*You'll probably have leftover pork after making this recipe. It freezes well, or use it again in another recipe, like these BBQ Pulled Pork Sliders