Cook rice according to package directions. Meanwhile, in a Dutch oven, heat 1 tablespoon margarine over medium-high heat. Whisk eggs until blended; pour into pan. Mixture should set immediately at edge. As eggs set, push cooked portions toward center, letting uncooked portions flow underneath. When eggs are thickened and no liquid egg remains, remove to a cutting board and chop.
In same pan, heat 1 tablespoon margarine over medium-high heat. Add Spam and onion; cook and stir until Spam is lightly browned, 6-8 minutes. Add mixed vegetables, garlic and pepper; cook until heated through. Stir in cooked rice, soy sauce and remaining 1/2 cup margarine; cook and stir until margarine is melted. Gently stir in eggs. If desired, top with sliced green onion.