Add the chickpeas to a large bowl with the baking soda and cover with twice the amount of water. The chickpeas will at least double in size, from 250g to approximately 525g after soaking for 12–24 hours.
Peel the garlic cloves and onion.
Drain and rinse the chickpeas, then add them to a food processor along with the other ingredients for the falafel. Blend on pulse speed for 2–3 minutes, until the mixture comes together but retains some texture. If you prefer smoother falafel, blend until smooth, though traditional falafel should have some chunkiness.
Heat the oil in a deep fryer or saucepan until it reaches 170°C, or until bubbles start to rise from the bottom.
While the oil heats, line a baking tray and shape the falafel mixture into small balls, about 3–4 cm in diameter. Compress them to hold their shape; they can be round balls or flattened like thick coins.
Once the oil is hot, carefully fry the falafels in 2–3 batches. Fry for approximately 4 minutes until golden and crispy. Transfer the falafel to a tray lined with kitchen paper to drain excess oil.
For the tahini cream, mix the tahini, yoghurt, lemon juice, garlic powder, and salt together until well combined and creamy.
Peel and finely dice the red onion, and finely dice the cucumber and tomatoes. Combine them in a bowl with a pinch of salt.