Preheat the oven to 350 F. Spray 4 squares of foil with cooking spray.
Place 1 cod fillet on each of the foil squares. Cut 1 lemon in half. Squeeze the juice from the lemon half over the fish. Cut the other half of lemon into slices, place over the fish and seal the foil.
Place in the oven and bake until the fish is opaque throughout when tested with the tip of a knife, about 20 minutes.
While the fish is cooking, remove the peel from the second lemon. Take care to cut only the peel and not the pith. Slice the peel into 1/4-inch-wide strips. Set aside.
In a small bowl, add the chicken bouillon granules and the hot tap water. Stir until the granules dissolve. Set aside.
In another small bowl, mix the butter and flour together. Transfer to a heavy saucepan. Stir over moderate heat until the butter-flour mixture melts. Add the bouillon to the butter mixture and continue to stir until thickened. Add the capers and remove from the heat. Serve over the fish and garnish with the lemon peel.