Place 1 chicken breast half between 2 pieces of plastic wrap or waxed paper. Working from center, gently pound chicken with flat side of meat mallet or rolling pin until about 1/4 inch thick; remove wrap. Repeat with remaining chicken breast halves. Sprinkle chicken with salt, oregano and pepper.
Heat oil in large skillet over medium-high heat until hot. Add chicken; cook 6 to 8 minutes on each side or until lightly browned and juices run clear. Remove from skillet; cover to keep warm.
In same skillet, cook chile pepper and onion 5 to 7 minutes or until chile pepper is crisp-tender, stirring occasionally. Meanwhile, in medium saucepan heat refried beans as directed on can.
Remove chile pepper mixture from skillet; keep warm. Heat same skillet over medium-high heat. Spread cut sides of rolls with margarine. Place rolls, margarine side down, in hot skillet. Cook 1 to 2 minutes or until golden brown.
To assemble sandwiches, place 2 to 3 tablespoons of the refried beans on bottom half of each bun. Top with chicken breast half, pepper mixture, tomato and lettuce; cover with top half of rolls.