Blend chili powder, cumin and salt.  Rub meat on all sides with spice mixture.  Put chopped onion and garlic on the bottom of your slow cooker.  Place meat on top.  Spoon ½ cup of salsa on top of meat.  Cook on low for 8 to 9 hours or on high for 3.5 to 4.5 hours.  The longer and slower you can cook it, the more tender it will be.

To Serve:  Remove meat from the slow cooker and place on a plate.  Use forks to shred the meat up.  Skim any fat from the cooking liquid and throw it away.  Return meat to juices and mix well.  Place meat on warm tortillas and top with cheese, tomato, cilantro, avocado and salsa.

To Prep for Freezer:  Chop Onions and garlic.  Cut meat into quarters.  Rub meat with spices.  Place meat, onion and garlic  into Gallon Size Freezer bag.  Label bag with marker and freeze.   Don't forget to keep 1/2 cup of salsa on hand to put on top after you remove the contents of the bag and place in the slow cooker.