Start by adding the rice, water, and salt to a saucepan and bringing it to a boil. Once boiling, reduce the heat to low, cover, and simmer for 15-20 minutes or until all of the water is absorbed and the rice is fluffy. Remove from the heat and set aside.
As the rice is cooking, heat a large metal or cast-iron skillet over medium heat. Wash and chop potatoes into bite-size pieces.* Slice the onion into 1/4-inch rings.
Once the skillet is hot, add the vegan butter. Swirl to coat. Add the potatoes to one half of the pan and the onions to the remaining half. Season with the salt and pepper, cover, and let cook for 4-5 minutes on one side. Then flip/toss to brown on the other side for 4-5 minutes, or until golden brown. Remove from the heat and set aside.
Add the beans to a small saucepan over medium heat and season with the cumin, garlic power, and chili powder. When bubbly, reduce the heat to low to keep warm.
To make the slaw, mash together the avocado and lime juice, then add the cabbage and jalapeno and toss to combine. Season with a pinch of salt and set aside.
To the cooked rice, add the lime juice and cilantro. Toss with a fork to combine.
To soften the tortillas, wrap in a damp towel and warm in the microwave for 30 seconds, (or in a 350 degree F oven (176 degrees C) for 1-2 minutes.
Add the fillings in any order, followed by sliced avocado and salsa (or hot sauce, if desired). Roll up, slice in half, and enjoy. Serve any extra potatoes, black beans, or rice on the side.