Warm a deep frying pan or wok over a medium heat for 1 min. Add 1 tsp oil and the lardons. Cook, stirring occasionally, for 7-8 mins, till the lardons are golden brown.
While the lardons fry, peel and finely slice the onions. Peel and finely chop the carrot. Peel and grate or crush the garlic.
Scoop the lardons out of the pan and pop them on a plate. Add the butter to the pan with the onions and a pinch of salt and pepper. Cook and stir for 5-8 mins till the onion is soft and a rich golden colour – if it is browning too much or too quickly, turn the heat down.
Stir the carrot, garlic and mushrooms into the pan. Cook and stir for 5 mins till the mushrooms are juicy.
Add the lardons back into the pan. Stir in the buckwheat and drop in the bay leaf. Crumble in the stock cube. Pour in 400ml boiling water. Give everything a stir to mix, then turn up the heat and bring to the boil. When the pan is boiling, turn the heat down and pop on a lid. Simmer for 12-15 mins till the water has been absorbed and the buckwheat is tender but still with a little bite.
While the buckwheat simmers, pick the soft fronds off the dill sprigs and roughly chop them. Roughly chop the rocket.
Taste the buckwheat and add a pinch more salt or pepper if you think it needs it. Fork in most of the dill and rocket. Spoon the buckwheat into warm bowls. Top with spoonfuls of yogurt and the last of the rocket and dill to garnish.