- Pre-heat the grill to high. Drain the tuna, reserving 1tbsp of the oil. Place the oil in a non-stick frying pan and heat. Add the spring onions and pepper, fry gently until the vegetables have softened (around 5 minutes!).
- Add the tuna, and heat through for a minute or two, stirring to make sure it doesn't stick.
- Remove from the heat. Add the mayonnaise, ketchup and lemon juice, and mix thoroughly.
- Top the cut sides of the muffin halves with the tuna mixture. Top with the cheese and place under the grill until the cheese melts.
Replace the muffins with 4 slices of wholegrain toast if you prefer!