1) Place the bread slices on a broiler pan. Divide the tuna mixture evenly among them, mounding it slightly. Sprinkle the cheddar cheese evenly over the tuna mixture.
2) Place under the broiler and broil (grill) until the tops just begin to bubble and are golden, 3 to 4 minutes. Watch carefully or the cheddar cheese may brown too much.
3) Transfer to individual plates and garnish with a lemon wedge and a parsley sprig.