Heat 2 tbsp olive oil in a large shallow pan over medium-high heat.
Add 4 boneless, skinless chicken thighs (cut into 2–3 cm pieces) and brown for 5–7 minutes. Remove and set aside.
Add 200 g cooking chorizo (sliced into 1 cm rounds) and cook for 3–5 minutes until crispy. Remove and set aside.
Reduce heat to medium. Add 1 large onion (finely chopped) and 1 red pepper (deseeded and chopped into 1 cm pieces); cook for 8–10 minutes until softened.
Stir in 2 cloves garlic (crushed) and 1 tsp smoked paprika; cook 1 minute until fragrant.
Add 300 g paella rice and stir for 2 minutes to coat grains.
Pour in 400 g tinned chopped tomatoes and 800 ml hot chicken stock. If using, crumble a small pinch of saffron threads into the stock. Stir and bring to a gentle simmer.
Arrange the browned chicken pieces evenly over the rice. Do not stir.
Simmer uncovered for 15–20 minutes until most liquid is absorbed and socarrat forms.
Scatter the cooked chorizo and 150 g frozen peas over the top. Cover and remove from heat; rest for 5–10 minutes.
Fluff rice with a fork. Season with salt and freshly ground black pepper. Garnish with fresh parsley and serve with lemon wedges.