Preheat the oven to 200C, fan-forced. Bring a small saucepan of water to the boil for the peas. Finely chop the onion. Cut the capsicum into small chunks.
Step 2 — Cook vegetables
Heat 2 tsp olive oil in an ovenproof medium deep frypan over high heat. (If your frypan is not ovenproof, you can cook the paella on the stovetop. Use a medium-low heat to prevent the rice burning on the base.) Add the onion, capsicum and 2 tsp Spanish seasoning*, season with salt and pepper and cook, stirring regularly, for 3 mins or until softened.
Step 3 — Cook peas and prep stock
While the vegetables are cooking, add the peas to the pan of boiling water, return to the boil and cook for 1 min. Drain. Crumble the stock cubes into a heatproof jug, add 250ml (1 cup) boiling water and stir to dissolve.
Step 4 — Cook paella
Add the tomatoes, stock, ½ tsp dried oregano* and ½ tsp sugar to the vegetable mixture. Stir and bring to the boil. Stir in the rice and bring to a simmer. Cover the pan with a lid or foil. Bake for 25 mins or until the rice is almost tender and the stock is absorbed.
Step 5 — Add greens and fish
While the paella is baking, trim the beans and cut into short lengths. Cut the fish into small chunks. Add beans and peas to the rice mixture, stir to combine, then put the fish on top. Cover and bake for a further 5 mins or until the fish is just cooked through. Remove from the oven and stand for 3 mins.
Step 6 — Get ready to serve
Meanwhile, finely chop the parsley, including the stems. Stir half the parsley into the paella. Taste, then season with salt and pepper. Scatter with the remaining parsley and serve with the aioli.