- low-calorie cooking spray
- ½ small onion, finely chopped
- 100g/3½oz Portobello mushrooms, finely chopped
- 250g/9oz extra-lean beef mince (under 5% fat)
- 2 tsp finely chopped fresh thyme (or ½ tsp dried thyme)
- freshly ground black pepper
- 1 Little Gem lettuce, leaves separated
- 120g/4½oz cherry tomatoes, sliced
- 1/3 cucumber, sliced
- Spray a small frying pan with oil and cook the onion and mushrooms over a medium heat for five minutes, or until well softened, stirring regularly. Tip into a heatproof bowl and leave to cool for five minutes.
- Add the beef, thyme and lots of ground black pepper. Mix well and form into two balls. Flatten into burger shapes, each around 2cm/¾in thick.
- Clean the pan and return to the hob. Spray with a little more oil and cook the burgers over a medium-low heat for 10 minutes, turning occasionally, until browned on the outside and cooked through inside.
- Serve the burgers with lettuce, tomatoes and cucumber.