Heat your oven to 200°C/Fan 180°C/Gas 6. Scrub the sweet potatoes and slice them into chips around 1cm thick. Pop them in a bowl and toss with ½ tbsp oil and some salt and pepper. Spread out on a baking tray in a single layer. Slide onto the top shelf of the oven and bake for 10 mins.
While the sweet potatoes bake, tip the dukkah onto a plate. Stir in the breadcrumbs. Separate the egg and put the yolk in a bowl and the white on a plate (see our tip on what to do with your egg yolk). Whisk the white to break it up. Brush a baking tray or roasting tin with ½ tbsp olive oil.
Tip the chicken leg into the beaten egg white and turn to coat, then tumble into the dukkah breadcrumbs and turn till well coated.
Lay the dukkah coated chicken on the greased baking tray in a single layer. Move the sweet potatoes down to a lower shelf. Slide the chicken onto the top shelf. Cook for 20 mins, till the sweet potato fries are tender and the chicken is golden and cooked all the way through – slice into a thick nugget to check there is no pink left in the flesh.
While the chicken bakes, pick any really thick stalks out of the watercress. Tumble it into a bowl.
Peel and crush the garlic. Pop in a bowl. Finely grate in the lemon zest. Squeeze in the juice from half the lemon. Add ½ tbsp olive oil and a pinch of salt and pepper. Whisk to combine. Taste. Add more seasoning if you think it needs it. Add to the watercress and toss to mix.
Serve the chicken nuggets with the sweet potato fries and the watercress salad, using the rest of the lemon as wedges for squeezing over the chicken.