Trim fat from roasts; cut meat into large chunks. Place in a 5- to 6-qt. slow cooker. Top with the chiles, onion, jalapenos, garlic, chili powder, cumin and seasoning blend if desired. Pour broth over all. Cover and cook on low for 8-9 hours or until meat is tender., Remove beef; cool slightly. Shred with 2 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.