Put the olive oil in a dutch oven and heat over medium.
Mix the paprika, cumin, salt, and pepper together and rub into beef shoulder on all sides. Put shoulder in dutch oven and sear on all sides. Remove from heat. Lift up shoulder and put onions underneath.
Mix together the remaining ingredients. You should have a thick sauce. Pour half of it over the beef and reserve the rest. Cover beef and put in oven for about 2 hours.
Remove from oven, turn beef over, and pour on remaining sauce. Cook an additional 2-3 hours, until beef shreds easily. Serve with the roasted onions and avocado tomatillo sauce.
Notes
Nutrition information does not include tortillas for serving.