Combine tomato, green onion, basil, and mustard in a 2-cup container; cover. Beat together eggs, milk, salt, and pepper in a bowl; cover. Pack ham and bread in separate self-sealing plastic bags; seal. Transport all items in an insulated cooler with ice packs.
Toast bread on both sides in a heavy medium skillet over campfire or medium heat; set aside. Melt margarine or butter in same skillet; pour in egg mixture. Cook over campfire or medium heat, without stirring, until mixture begins to set on the bottom and around edge. Sprinkle with ham. Lift and fold the partially cooked eggs with a spatula or a large spoon so the uncooked portion flows underneath. Continue cooking for 2 to 3 minutes or until eggs are cooked through, but are still glossy and moist. Remove from heat.
Divide the egg and tomato mixtures among the toast slices. Makes 4 servings.