Cook the brown rice according to the packet instructions (20-25 minutes).
Whilst the rice is cooking toast the almonds by tipping the almonds in a saucepan so they are in a very shallow even layer. Heat on a low-medium heat for 1-2 minutes, tossing occasionally, until just turning golden. Remove the almonds from the pan to cool in a small bowl.
Prepare the pesto dressing by whisking the Dijon and lemon juice along with some salt and pepper in a small bowl until emulsified and thickened.
Whisk in the pesto then drizzle in the olive oil whisking all the time until the dressing has come together. Allow to sit and the flavours to mingle whilst you are waiting for the rice to finish cooking.
Drain the rice once cooked then tip out onto a shallow baking tray to cool whilst you are chopping the rest of the salad ingredients.
Prepare the red onion by peeling and dicing very small then covering in a small bowl with the juice of half the lemon and a pinch of sugar and salt for 10 minutes.
Once the rice has been cooling for 10 minutes then tip into a large mixing bowl and toss with the pesto dressing. Allow the rice to absorb the dressing whilst you prepare the rest of the vegetables.
Dice the celery, pepper and quarter the cherry tomatoes. Then de-seed the cucumber by halving lengthways and scooping out the seeds with a teaspoon. Dice the remaining cucumber. Then finely chop the parsley leaves and dill.
Drain the red onion from its pickling mixture then mix with the dressed rice, along with the rest of the salad ingredients (save some flaked almonds to top the salad upon serving) and toss together well.
Cover and store the salad in the fridge until needed.
When ready to serve transfer to a large salad bowl and sprinkle over the flaked almonds.