Combine onion, garlic, beef, salt, cumin, chili powder, chopped chipotle peppers, red pepper and oranges in crock pot. Cook on high for 5 hours or low 7-8.
In skillet over medium heat lightly brown and warm tortillas. Add lettuce to tortillas. Remove oranges from crock pot and with slotted spoon split the beef between the floured tortillas. Top with cilantro, tomatoes, black olives, avocado and sour cream.