Heat the butter or oil in a skillet over medium heat. Add the celery and zucchini and cook, stirring frequently, for 2 minutes.
Add the ground beef, tomato paste, salt, and spices. Continue to cook, stirring frequently until the beef is completely cooked through. Remove from the heat.
Assemble the tacos. The lettuce leaves will act as the tortillas. Place half of the ground beef on each lettuce leaf, and top with the grated cheese and cilantro.