Heat your oven to 180°C/Fan 160°C/Gas 4. Tip the quinoa into a sieve and rinse it under cold water for 1-2 mins, stirring it with your hand.
Tip the quinoa into a small pan. Pour in 300ml boiling water. Cover. Bring to the boil, then turn the heat down and simmer for 12-15 mins till all the water has been absorbed and the
grains are tender.
While the quinoa simmers, slice the stalks off the mushrooms and finely chop them. Pop them in a bowl. Peel and finely chop the garlic. Finely grate the zest from the lemon. Add them to the mushroom stalks.
Pick the leaves off the thyme sprigs. Add most of them to the bowl (keep a pinch back for garnishing).
When the quinoa is cooked, drain it (if necessary) and add half of it to the bowl. Add a pinch of salt and pepper and stir to mix. Taste the mixture and add more salt and pepper if you think it needs it. Set the remaining quinoa side for later.
Put the mushrooms in a small roasting tin or on a baking tray. Heap the quinoa stuffing in the mushrooms. Pop the cherry tomatoes on the tray alongside the mushrooms. Bake in the oven for 20 mins till the mushrooms are golden and the tomatoes are just bursting.
While the mushrooms bake, juice half the lemon. Whisk the juice with 2 tsp olive oil and a pinch of salt and pepper to make a dressing. Toss the salad leaves and remaining quinoa with the dressing.
Serve the baked mushrooms with the salad and tomatoes. Slice the remaining lemon half into wedges for squeezing.