Trim fat from roasts; cut meat into large chunks. Place in a 5-qt slow cooker.
Top with the chilies, onion, jalapenos, garlic, chili powder, cumin and seasoning blend if desired. Pour broth over all. Cover and cook on low for 8-9 hours.
Remove beef; cool slightly. Shred with two forks. Cool cooking liquid slightly; skim fat.
In a blender, cover and process cooking liquid in small batches until smooth. Return liquid and beef to slow cooker; heat through. Place 1/3 cup beef mixture on each tortilla. Top with tomatoes, lettuce and cheese if desired. Fold in ends and sides.