Preheat the oven to 220C (fan).
Cook the chicken: Season the chicken drumsticks with salt and roast them for 35 minutes in the oven at 220C. If you use boneless chicken pieces, fry them in a skillet and set them aside. Prepare the soffrito: (Note 1) Fry the onion until translucent; add chorizo and cubbed pepper (not the slices) and continue frying for 1 minute.
Stir in the paella seasoning and tinned tomatoes. Reduce liquid from the tomatoes by cooking the soffrito for another 3 - 4 minutes on medium/high heat.
Add the rice into the sofrito and stir well until it's evenly coated with the sauce (if you need to transfer the ingredients to an oven-safe dish, now is the time to do so).
Turn the oven temperature to 240C.
Assemble the paella: Pour the hot stock (Note 2) over the rice coated with soffrito (in the oven-proof pan or tray), and with a spatula or wooden spoon, distribute the ingredients evenly across the base of the dish.
Nestle in the remaining ingredients - chicken drumsticks, king prawns, and bell pepper slices.
Lay lemon over the top.
Cook paella: Cook paella for 10 minutes in a preheated oven to 240C; turn the temperature down to 220C and cook for an additional 10 minutes or until the rice absorbs most liquid. (Note 3)
Let the paella rest for 5 minutes before serving.