Melt margarine in large skillet on medium-high heat. Add meat; cook and stir 2 to 3 min. or until evenly browned. Stir in onions and water; cover. Simmer 30 min., stirring occasionally and adding more water if needed. Add green peppers and mushrooms; stir. Simmer, covered, 10 min., stirring occasionally. Meanwhile, cook pasta as directed on package, omitting salt.