In small saucepan, bring 3/4 cup (175 mL) of the vegetable broth to boil. Pour over the textured vegetable protein (TVP) in bowl; cover and let stand for 10 minutes.
Meanwhile, in large skillet, heat sunflower oil over medium heat; stir-fry onion, celery and garlic for about 5 minutes or until softened. Add chili powder, cumin, coriander, oregano, chipotle powder and salt. Add TVP; cook, stirring, for 2 minutes.
Stir in tomatoes and remaining broth; bring to boil. Reduce heat and simmer for about 10 minutes or until thickened.
Fill each taco shell with about 1/4 cup (50 mL) filling. Top with lettuce, tomatoes, avocado (if using) and cheese.