Cook chopped potato in a saucepan in boiling water to cover, 10 to 12 minutes, or until tender. Drain well. Coat a large nonstick skillet with cooking spray; place over medium-high heat until hot. Add potato, tomato, green onions, pepper and salt; sauté until onion is tender. Pour egg substitute over vegetable mixture. Cover skillet; cook over medium-low heat 15 minutes, or until set. Sprinkle with cheese. Cover; cook 2 minutes, or until cheese melts. Cut into 6 wedges and serve immediately. Garnish with green onions, if desired.