Heat the oven to 220C/200C fan/gas 7. Combine the tomatoes, stock, paprika and saffron in a large heatproof jug, then microwave for 5 mins on high, or until steaming hot. Or, heat in a pan on the hob.
Put the onion and garlic in a large ovenproof frying pan or roasting tin, drizzle over the olive oil and stir to coat. Roast for 20 mins, or until the veg is starting to brown.
Stir in the rice, chicken, chorizo and hot stock mix. Season and bake for 20 mins (don’t cover the pan).
Gently stir in the peas, dot over the prawns and press the mussels in, hinged-side down, so they’re standing up. Arrange the lemon wedges around the edge, if using. Bake for 5-10 mins more until the rice, chicken and prawns are cooked, and the mussels have opened (discard any that stay shut). Check for seasoning, and serve.