Top 2 slices of the bread with cheese. Place remaining slices of bread over cheese. Spread top of bread slices with half of the margarine.
Place sandwiches, margarine side down, in large skillet. Cook over medium heat for 2 to 4 minutes or until golden brown. Spread top of sandwiches with remaining margarine. Turn sandwiches; cook 2 to 4 minutes or until golden brown. Remove sandwiches from skillet; place on cutting board. Cool 5 minutes.
Cut sandwiches into strips or triangles. Wrap in plastic wrap or place in food storage plastic bags. Store in refrigerator.
Pack cold wrapped sandwiches in 2 lunch bags with ice packs. Divide salsa into 2 small plastic containers with lids. Place in lunch bags.
At lunch time, dip sandwiches in salsa.