Place chuck roast, onion, chipotles, chili powder, cumin, salt, pepper, and beef broth in slow cooker. Cook on low for 8 hours or on high for 5 hours. After the meat is tender, shred into bite size pieces.
Heat oven to 400 degrees. Place tomatillos (remove husk) on baking sheet and bake for 12-15 minutes or until soft. Place in blender or food processor with cilantro, jalapeno, lime juice, salt and sugar. May add more sugar depending on preference. The sugar cuts the acidity of the tomatillos. Let chill.
Top two corn tortillas with beef, queso fresco, avocado, and tomatillo salsa.
*May soften corn tortillas by wrapping in slightly damp paper towel and placing in microwave for 20-30 seconds.