Coat a large nonstick skillet with cooking spray; place over medium-high heat until hot. Add sausage, and cook 5 minutes or until browned, stirring often. Remove from skillet, and set aside.
Wipe skillet dry with a paper towel.
Coat skillet with cooking spray; add margarine. Place over medium-high heat until margarine melts. Add green pepper and onion; saute 8 minutes or until vegetables are tender. Return sausage to skillet; sprinkle Greek seasoning over sausage. Cook 1 minute or until thoroughly heated, stirring occasionally. Spoon sausage mixture evenly into buns. Serve warm.