Scrub potatoes; prick each potato several times with a fork. Bake at 400° for 1 hour or until potatoes are done.
Coat a large nonstick skillet with cooking spray; add margarine. Place over medium-high heat until margarine melts. Add red pepper and green onions; saute 3 minutes or until tender. Stir in corn, chili powder, salt, and pepper; saute 3 minutes or until tender. Remove from heat, and let cool. Stir in sour cream and minced cilantro. Set aside.
Allow potatoes to cool to touch. Cut potatoes in half lengthwise. Carefully scoop out pulp, leaving about 1/8-inch-thick shells. Cut each shell in half lengthwise. Reserve potato pulp for another use.
Place shells, skin side down, on an ungreased baking sheet; spray shells lightly with cooking spray. Bake at 425° for 15 minutes or until crisp. Spoon corn mixture evenly into shells; sprinkle evenly with cheese. Broil 5 1/2 inches from heat (with electric oven door partially opened) 2 to 3 minutes or until cheese melts. Garnish with cilantro sprigs, if desired. Serve immediately.