Wash the sweet potatoes and slice in the processor. Put into the lidded pan with a pinch of salt, then cover with boiling water and the lid. Put the prawns into a roasting tray, squash over the unpeeled garlic through a garlic crusher, then toss with the Cajun seasoning, 1 tablespoon of oil and the thyme sprigs. Spread out in a single layer and pop on a high heat for a couple of minutes to crisp the bottoms of the prawns up, then place under the grill until the tops are sizzling, golden and crispy.
Deseed and roughly chop the peppers and put into the frying pan with 1 tablespoon of oil. Trim and slice the celery, spring onions and chilli, and add to the pan along with the sweetcorn and paprika. Season with salt and pepper and keep things moving.
When cooked through, drain the sweet potatoes in a colander. Return to the pan and mash well. Grate in the cheese, mix well and season to taste. Scatter the veg over the mash and serve with the crispy prawns and lemon wedges.
You can use fresh sweetcorn instead of frozen when it’s in season. Griddle the cobs on the barbecue until lovely and charred, stand the cobs on one end and carefully slice off the kernels and mix into the veg to add a lovely smokiness.