Sift the besan, paprika, cumin and baking powder into a bowl, add the pepper and mix together. Make a well in the centre. Gradually add the soda water and whisk until it is a smooth batter. Season to taste with salt. Cover and leave to stand for 30 minutes.
Meanwhile, for the salad dressing, in a bowl, whisk together the lemon juice, olive oil and garlic.
Fill a deep, heavy-based saucepan one-third full with vegetable oil and heat until a cube of bread browns in 15 seconds. Dip the squid rings in the batter, add to the oil, in batches, and cook for 30–60 seconds until golden brown. Remove with a slotted spoon and drain on kitchen paper.
Add the parsley, red onion and tomatoes to the dressing and toss well to mix. Top with the battered squid and serve immediately.