Mix pesto with mayonnaise and lemon juice. Season to taste. Split chicken breasts on a flat fillets, sprinkle with salt and pepper. Fry in a pan for 2-3 minutes on each side, so that chicken remains juicy. Prepare fries according to package instructions.
Brush toasts with pesto. Put a few leaves of lettuce, and the chicken fillets on one of them. Cover with second toast. Serve with fries.
Use toasts instead of bread & add a slice of favourite cheese to the sandwich.