If you are in Phase 1, wrap the cooked beef in Boston or bibb lettuce leaves to serve. If you are in Phase 2, you can also wrap them in low-carb tortillas (no more than 4 grams of Net Carbs per tortilla), but don't forget to count the additional carbs.
Trim fat from beef. Place beef, salsa, garlic, green onions, jalapeño, chili powder, cumin and salt in a slow cooker. Cover and cook on low 8 hours, or until beef is very tender.
Remove beef and shred, using two forks. Mix beef with 1/2 cup cooking juices before serving.
In order to calculate Net Carbs of any whole food item, it's a simple calculation based on the Nutrition Facts panel:
Total Carbohydrates - (Minus) Dietary Fiber = (Equals) Net Carbs
For low carb products sweetened with sugar alcohols (ie: glycerin, maltitol, etc), refer to the Nutrition Facts panel of the product:
Total Carbohydrates - (Minus) Dietary Fiber - (Minus) Sugar alcohol = Net carbs
This reflects the fact that Dietary Fiber doesn't impact blood sugar levels. Sugar alcohols also have a negligible impact on blood sugar, they too are subtracted from total carbs to yield the Net Carb count.