Heat your oven to 220°C/Fan 200°C/Gas 7. Place 1 tsp fennel seeds in a mortar and grind with a pestle, or use a small bowl and a jam jar to roughly crush them.
Add 1 tsp each ground cumin and smoked paprika and a pinch of salt to the fennel seeds. Peel and grate in the garlic. Finely grate in the lemon zest. Stir in 1 tbsp oil to make a paste. Set aside.
Place the chicken breasts between two sheets of cling film or baking paper. Bash with a rolling pin to flatten them slightly so they are evenly thick, around 2-3 cm. Rub the spice paste into the chicken, coating it all over. Place the chicken breasts on a large baking tray or in a roasting tin. Set aside.
Scrub the sweet potatoes and chop them into 1cm-thick slices, then cut the slices into 1cm-thick chips (no need to peel the spuds).
Tip the chps into a bowl with 1 tbsp oil and some salt and pepper. Toss to coat in the seasoned oil. Spread the sweet potatoes on the tray with the chicken. Roast for 25 mins.
After 25 mins, add the cherry tomatoes to the baking tray. Roast for another 10 mins till the chicken breasts are cooked through, the sweet potatoes are tender and the cherry tomatoes have just burst. Serve straight away with wedges of the zested lemon for squeezing.