1. Bake potatoes. IN THE OVEN: Preheat oven to 375°F. Scrub potatoes and pat dry. Prick all over with a fork. Rub lightly with vegetable oil; sprinkle with salt. Place on oven rack and bake until a knife inserted in center of potato slides in easily, about 1 hour to 1 hour 15 minutes. IN THE MICROWAVE: Scrub potatoes. Prick all over with a fork. Place potatoes on a microwave-safe plate; microwave on high 4 minutes. Turn potatoes over and microwave until a knife inserted in center of potato slides in easily, 6 to 8 minutes longer. Cooking time will vary depending on the microwave.
2. In a skillet over medium heat, cook beef and onion until meat has browned. Drain off fat. Add garlic; sauté 1 minute. Add chili powder, cumin, oregano and 1/2 tsp. salt; sauté 2 minutes. Stir in tomato sauce and beans. Bring to a boil. Reduce heat; simmer 20 minutes.
3. Cut a deep cross in tops of potatoes; squeeze open. With a fork, fluff up centers. Season with salt and pepper. Top potatoes with beef mixture, avocado and scallions.