Melt margarine in a large nonstick skillet over medium heat. Add squash, bell pepper, onion, and jalapeno. Simmer to your desired level of doneness, 5 to 10 minutes. Add cubed tofu. Cook and stir until heated through, about 2 minutes. Add soy sauce and garlic powder; cook about 5 minutes more.
Wrap tortillas in a moist paper towel and heat in the microwave on high until soft, about 30 seconds.
Spread a thin layer of vegan sour cream on each tortilla. Add tofu and vegetable mixture and roll up, burrito-style.