Combine rice, water (13/4cups for white and 21/2cups for brown) and salt to taste. Bring to a boil, lower the heat, cover and cook till the rice is tender. Remove from heat and set aside. After a couple of minutes, stir in lime juice and cilantro.
In a small saucepan, combine lack beans, cumin, garlic powder and chili powder. Add 1/4cup of water and simmer till bubbling. Cover and keep warm.
Microwave the potatoes for 3~4 minutes or until just tender.
Heat oil in a nonstick or cast iron pan, add the potatoes to one half of the pan and the onions to the other half. Season with salt and pepper and cook for 4~5 minutes or until slightly browned. Toss together around and cook till lightly browned all over. Remove and heat and set aside.
Warm the tortilla until pliable. Pile up the rice, beans and potatoes, followed by salsa, sour cream and cheese. Roll it up and cut in half. Enjoy right away or pack up for lunch.