Preheat the oven to 200°C. Place the chicken in a large roasting tin.
In a small mixing bowl, combine the butter, paprika, lemon zest, half the oregano, salt and pepper and one garlic clove (minced) until creamy. Spread most of the paste evenly under the breast skin, in the cavity and all over. Season with salt and pepper. Put half of the lemon in the cavity.
Wrap the tin with foil and roast the chicken for 20 minutes.
Meanwhile, cut the potatoes in half; deseed and cut the peppers into wedges; cut the onion into wedges; chop the chorizo into chunks; and lightly smash the garlic (unpeeled). Put everything in a mixing bowl, add the remaining oregano, butter paste (and a little olive oil, if needed). Season with salt and pepper, then toss together.
Take the chicken out of the oven after 20 minutes and remove the foil. Turn down the heat to 180°C.
Tilt the chicken slightly to release the juices from the cavity into the pan, then baste the chicken with this.
Scatter the mixed veg and chorizo around the chicken and roast for another 45-50 minutes or until everything is cooked through. Check the chicken by piercing between the thighs and carcass with a skewer - it's ready when the juices run clear.
Let the chicken rest (covered) for 10 minutes before carving.
Serve with the chorizo, vegetables and the pan juices.