Heat the oil in a large skillet over medium heat. Cook the pumpkin in the heated oil 2 to 3 minutes. Stir in the vegetable stock, cumin, salt, and pepper. Cook until the pumpkin cubes are easily pierced through with a fork, 5 to 7 minutes. Fill warm tortillas with pumpkin; top with tomato, onion, avocado, and cilantro as desired.
