Peel and finely slice the onion. Pluck any soft fronds off the fennel bulb, then halve it. Set 1 half aside (see our tip) and finely slice the other half.
Warm a large, deep frying pan or wok over a medium heat for 2 mins. Add 1 tbsp oil, the sliced onion and fennel and a pinch of salt and pepper. Pop a lid on the pan (or use a baking tray if you don’t have a lid) and sweat the veg for 8 mins, stirring a few times, till soft and pale golden.
While the veg fry, halve the pepper and scoop out the seeds and pith. Finely slice it. Peel and crush or grate the garlic. Halve the chilli, flick out the seeds and white pith for less heat, and finely chop it.
Stir the pepper, garlic and chilli into the veg with 1 tsp fennel seeds. Cook and stir for 2 mins till the pan smells aromatic. Pour in 250ml boiling water, pop the lid back on the pan and let the pan simmer for 10 mins. Stir now and then.
While the veg simmer, tip the bulgar wheat into a heatproof bowl. Pour in 300ml boiling water. Cover the bowl with a plate and set aside for 10 mins to soak. The bulgar will suck up all the water and cook. While the bulgar soaks, grate the zest from the lemon. Finely chop the chives.
Take the lid off the pan and give the fennel sauce
a stir. Taste and add a pinch more salt and pepper if you think it needs it. Slide in the plaice fillets, skin side down. Pop the lid back on and cook for 3-4 mins. The plaice will be opaque and flake easily when pressed with a fork.
Crumble half the pack of feta. Scatter into the pan over the plaice. Pop the lid back on and keep the pan on the heat for 2-3 mins to just melt the feta.
Fluff the bulgar wheat with a fork, draining off any excess water if you need to, and stir in most of the lemon zest and the chopped chives. Squeeze in the juice from half the lemon. Spoon the bulgar wheat onto 2 warm bowls. Lay a plaice fillet on top and spoon over the sauce. Scatter over the fennel fronds, the remaining chopped chives and lemon zest. Serve with the last of the lemon sliced into wedges for squeezing.