Remove stems and seeds from ancho chilies. Place chilies in a saucepan, cover with water and cook until soft, about 10 minutes. Drain chilies, let cool, then puree in a food processor or blender. While chilies cook, cut up two tortillas into small pieces. In a large saucepan, saute tortillas, onion and garlic in 2 teaspoons canola oil until onions are soft. Add ancho pepper puree or chili powder, chicken stock, tomato puree, cumin, oregano and salt to saucepan. Bring soup to a boil, reduce heat and simmer 30 minutes. Puree soup in a food processor and return it to saucepan. Stir in lime juice and reheat. Slice remaining tortillas into 1/4-inch x 2-inch strips. Heat remaining oil in a medium skillet. When oil is hot, add tortilla strips and saute until crisp, about 2 minutes. Transfer tortilla strips to a paper towel to drain. Ladle soup into bowls and top with tortilla strips, cheese and garnishes, as desired.