In a small bowl, combine chili powder, cumin, paprika, Italian seasoning, and salt. Rub all over chuck roast and place in a 5-qt slow cooker.
In a medium skillet over medium-high heat, saute garlic in oil until just fragrant, about 2 minutes. Add chipotle, tomato paste, and gradually whisk in broth until smooth. Bring mixture to a simmer then remove from heat. Pour over beef. Cook beef on low 6-8 hours until beef easily shreds with a fork. Once beef is cooled enough to handle, shred with two forks, season with salt and pepper to taste, and transfer shredded beef back to crockpot to keep warm.
Make the salsa: In a small bowl, combine all salsa ingredients. Season with salt and pepper to taste. Refrigerate until ready to serve.
Make the avocado crema: In a food processor, combine all avocado crema ingredients and process until smooth and creamy. Season with salt and pepper to taste.
Just before serving, assemble the tacos: Place shredded beef in tortillas, top with greek salsa and drizzle with avocado crema. Enjoy!