Place the frozen veg in a food processor and let them defrost for around 15 minutes.
Add the coriander (stalks and all), flour, cumin and cayenne, season well with sea salt and black pepper, then blitz to a rough paste. Pulse in the sesame and sunflower seeds until combined.
Divide the mixture and shape into 4 equal-sized patties, roughly 2cm thick. Place on a lightly flour-dusted tray, turning them in the flour to coat. Firm up in the freezer for 10 minutes, then transfer to the fridge.
Preheat the oven to 160ºC/325ºF/gas 3, while you make the vegan mayo and onion rings.
For the mayo, trim and roughly chop the spring onions and chilli (deseeded if you like) and place in a blender. Peel and add the garlic, along with the chickpeas, mustard, tomato paste, brandy, lemon juice and a good pinch of salt and pepper. Blitz well to combine, then, with the blender still running, slowly pour in 4 to 5 tablespoons of extra virgin olive oil until smooth and the same consistency as mayonnaise.
For the onion rings, peel the onion and slice horizontally into 2cm-wide rounds. Separate into rings, then place in a bowl with the vinegar and a pinch of salt. Leave for 5 minutes.
Meanwhile, combine the flour and baking powder in a bowl, then gently whisk in the ale until smooth, thick and coating the back of a spoon nicely.
Place a medium, deep pan over a high heat, pour in the sunflower or sunseed oil and allow to heat up. To test if the oil is hot enough, drop a piece of bread into the pan – if it floats to the surface, sizzles and turns golden, it’s about right.
Drain the onions, dust a handful of them with flour until lightly coated, then dip them into the batter. Remove with a slotted spoon and allow any excess batter to drip off, then carefully lower into the hot oil.
Cook for around 1 minute, or until golden and crisp, turning halfway with the slotted spoon. Transfer to a double layer of kitchen paper to drain, then repeat with the remaining onion.
When you’re ready, cook the burgers in 1 tablespoon of oil in a large frying pan on a medium heat for 10 to 12 minutes, or until golden and cooked through, turning halfway and pressing down with a fish slice to get them nice and crispy.
Transfer to a baking tray, then pop into the oven while you prepare the remaining ingredients.
Finely shred the lettuce and mix with half the vegan mayo (keep the rest in the fridge for up to 2 days). Slice the tomatoes and place on a plate lined with kitchen paper.
Sprinkle over a little salt and pick over the basil leaves. Top with another piece of kitchen paper and pat lightly to remove any excess water.
Slice the gherkins lengthways, then halve and destone the avocado. Scoop out the flesh, cut into slices, then squeeze over the lime juice.
Halve the burger buns and toast on a hot griddle pan or under the grill.
Once ready, pile the dressed lettuce and sliced tomatoes and basil on to the burger bun bases. Pop the burgers on top, snip over the cress, then layer over the avocado, gherkins and crispy onion rings.
Add a good squeeze of ketchup to the burger bun lids, place them on top, squeezing down gently, then tuck in.