Heat your oven to 200°C/Fan 180°C/Gas 6. Pop the pork belly strips in a large roasting tin and roast in the oven for 20 mins.
While the pork belly strips roast, tip the porcini mushrooms into a measuring jug and top up with 300ml boiling water. Set aside to soak.
Slice the leaves off the radishes (see our tip below), then rinse the radishes and shake dry. Slice them into halves or quarters and place in a bowl. Chop the mint leaves. Finely slice the spring onions, trimming off the roots. Stir both into the radishes along with the zest and juice of the lemon and a little salt and pepper. Set aside – the lemon juice will lightly pickle the radishes.
When the pork has had 20 mins, remove the roasting tin from the oven and spoon away most of the fat. Tuck the portobello mushrooms around the meat and drizzle over 1 tbsp olive oil. Sprinkle the thyme leaves over the mushrooms, season well and return to the oven for a further 20 mins.
While the pork and mushrooms roast, peel and grate the garlic clove. Pour 1 tbsp olive oil into a pan and bring to a medium heat. Add the garlic and some seasoning and fry for 1 min, stirring frequently. Stir in the buckwheat and pour in the porcini and liquid. Bring to the boil, then cover the pan with a lid, reduce the heat and simmer for 10 mins or till the grains are just tender.
When the buckwheat is cooked, stir in the baby leaf spinach. Keep cooking on a low heat, till the spinach has wilted and all liquid has been absorbed. Taste and add salt and pepper if you think it needs it.
Spoon the buckwheat onto 2 warm plates and top with a chunk of roast pork belly each. Pop the mushrooms on the side and spoon over the quick pickled lemony radishes to serve.