Make mango avocado salsa and refrigerate until ready to serve.
Heat a large non-stick skillet over med-high heat.
Add 2 lbs ground beef and cook, stirring occasionally until cooked through (5 minutes).
Use a spoon to skim off and discard most of the excess fat, leaving about 2 to 3 Tbsp in the pan.
Add 2 cans of tomatoes, 1 tsp chili powder, and 1 tsp salt.
Continue to cook until beef is fully cooked, sauce slightly reduced, and most of the tomato liquid has evaporated (7 to 10 minutes).
Before serving, slightly grill both sides of the corn tortilla until just hot (15 to 30 seconds per side).
Remove to a plate and cover loosely with foil to keep warm.
To serve, place a heaping spoonful of beef over each tortilla, top with lettuce, mango salsa, sprigs of cilantro, sour cream, and a sprinkle of chili powder if desired. Squeeze fresh lime juice just before eating.