Peel and crush or grate the garlic. Pop it in a dish. Grate in the zest from the lemon. Halve the lemon and squeeze in the juice from one half. Add a pinch of salt and pepper. Stir to mix, then add then chicken and turn to coat in the marinade. Set aside to marinate for 15 mins.
Put a medium pan of water on to boil. Peel and halve the shallots. Trim the carrots, peel them and slice them into thin batons about as big as your little finger. Trim any dry ends off the Kalettes®.
When the water is boiling, drop in the Kalettes® and the carrot batons. Simmer for 2 mins to just blanch them, then drain. Set aside.
Crumble the stock cube into a jug and stir in 150ml boiling water. Empty the water pan out and wipe dry. Tip the buckwheat into the pan and set over a medium heat. Toast for 4-5 mins, stirring, till the buckwheat starts to brown. Carefully pour in the stock a splash at a time (it will splutter), then pop a lid on the pan. Simmer for 12-15 mins till the stock has been absorbed and the buckwheat is tender. When the buckwheat is cooked, take off the heat and leave in the pan, with the lid on, to keep warm.
While the buckwheat simmers, put a large griddle or frying pan on a high heat. Warm for 2 mins. Add ½ tbsp oil to the pan with the shallots, carrots and Kalettes®. Fry for 5-6 mins, tossing the veg in the pan, till lightly charred and tender.
Scoop the veg into a dish or bowl and cover with foil to keep warm (you can also pop it in the bottom of your oven, set to its lowest temperature).
Add another ½ tbsp oil to the pan. Lift the chicken fillets out of the marinade. Add it to the pan. Fry for 10 mins, turning often, till golden brown all over and cooked through – check by slicing into the thickest part of the chicken fillets. There should be no pink.
Spoon the buckwheat into warm bowls. Top with the griddled veg, baby leaf spinach and the griddled chicken. Serve with wedges of the remaining lemon half for squeezing.