1. In 12-inch skillet over medium-high heat, cook ground beef, onion, and potatoes until meat is browned and onion and potatoes are tender, turning occasionally with pancake turner and adding salad oil if necessary. Stir in salt, oregano, pepper, 1 teaspoon chili powder, 1/2 cup kidney beans, and half of tomato sauce; remove skillet from heat.
2. Cut each green pepper lengthwise in half; remove seeds. Stuff green-pepper halves with meat mixture; set aside. In same skillet, stir water, remaining kidney beans, remaining tomato sauce, and 1/2 teaspoon chili powder.
3. Arrange green peppers in sauce in skillet; over high heat, heat to boiling. Reduce heat to low; cover and simmer, stirring occasionally, until peppers are tender, about 25 minutes.