Preheat oven to 200°C fan-forced (220°C conventional).
Place capsicums in a baking tray lined with foil.
Cut cauliflower in florets and place in another baking tray lined with baking paper or foil.
Place both trays in oven. Turn capsicums as the skin starts to darken.
While the vegetables roast, slice onion and place in a heat-proof bowl. Cover with boiling water and let sit for 5 minutes. Drain and cover with red wine vinegar and a pinch of salt.
Remove the cauliflower tray once the florets have browned and softened.
Remove the capsicum tray once the skins are mostly charred.
Place capsicums in a bowl and cover with cling wrap. Let sit for 10 minutes to let the skins soften. Once the time is up, peel the skins off taking care of not burning yourself. Cut capsicums open, remove the stems and seeds and slice in strips.
Serve baby spinach and roasted vegetables on plates or bowls. Scatter onions on top, with some of the pickling vinegar to taste.
If your canned fish is packed in water, drain the water and serve on top of vegetables. Drizzle with extra virgin olive oil.
If your canned fish is packed in extra virgin olive oil. serve fish on top of vegetables and drizzle with the oil in the can.
Season with salt, pepper and chilli flakes if using.