Step 1 Boil, steam or microwave sweet potato chunks until tender; drain and leave to cool slightly.’
Step 2 Meanwhile, place half of the dill leaves in a small salad bowl. Chop remaining dill roughly and place in a medium bowl. Add sliced onion and cucumber to small salad bowl with chickpeas and gherkin halves; set aside.
Step 3 Place cool sweet potato in medium bowl of chopped dill; mash roughly with a fork. Add tuna, breadcrumbs and lemon zest to bowl; stir to combine.
Step Stir beaten egg through mixture. Wet hands to shape 2 patties, adding more breadcrumbs if mixture is too moist. Coat patties evenly with sesame seeds.
Step 4 Spray a large non-stick frying pan with olive oil and set over high heat. Add patties and cook, flipping carefully, for 2–3 minutes per side, or until golden brown.
Step 5 Add lemon juice and olive oil to small salad bowl; toss.
Step 6 Serve tuna and sweet potato patties with chickpea–dill salad and lemon wedges.