Grate the zest of the lemon and set aside to use later in the recipe. Peel the red onion and slice it as thinly as possible. Slide the onion into a small bowl and squeeze over the lemon juice. Sprinkle in a little salt and pepper and scrunch well together. Set aside.
Warm a large frying pan to a medium heat. When the pan is hot, scatter in the breadcrumbs. Sprinkle in the lemon zest and a pinch of salt and pepper. Cook for 3-4 mins, stirring frequently, till golden and toasted. Tip the breadcrumbs into a bowl.
Trim the bases of the lettuces, and slice into thin wedges. Trim the tops off the courgettes, and use a vegetable peeler to create long ribbons. Slide both into a large salad bowl. Fold in the lamb's lettuce.
Drain the lentils through a sieve, and rinse well with cold water. Shake as dry as possible, and tip into the bowl with the salad.
Pour 2 tbsp oil into the empty pan used for the breadcrumbs and bring to a medium-high heat. Scatter in the sliced garlic and cook quickly for 1-2 mins, turning once or twice, till the garlic is lightly golden.
Tip the pickled onions and lemony juices over the salad. Pour over the garlic and infused oil. Stir well with salad spoons to evenly dress. Taste a little bit of salad and add more salt and pepper if needed.
Arrange the salad onto plates and finish with generous sprinklings of crispy breadcrumbs.