Heat oven 220 degrees Celsius or equivalent.
Add 1 tbsp oil to a large, ovenproof lidded pan or dish and heat over high flame. Season the chicken with ¾ tsp of salt and ½ tsp of pepper, then add to the hot oil, skin-side down. Cook for 7 minutes, without turning, to brown well.
Turn the heat down to medium-high, then stir in the onion and turn over the chicken. Cook for 5 minutes, until the onion has softened and is lightly browned. Add the tomato puree, garlic and 1 tablespoon thyme, and cook, stirring the paste into the onions, for 2 minutes, until fragrant and everything is nicely browned.
Add the boiling water, ½ tsp salt and ¼ tsp pepper, then add the spaghetti, stirring to submerge and evenly distribute. Use tongs to lift the chicken pieces so they sit on top of the spaghetti, skin-side up. Bring to a simmer, cover with a lid and transfer to the oven for 30 minutes, until the liquid is absorbed.
While the pasta is in the oven, in a small bowl, mix together the Parmesan, breadcrumbs, parsley, lemon zest and remaining 1 tablespoon thyme.
After the pasta has baked for 30 minutes, remove it from the oven and reset the temperature to a grill setting. Sprinkle the Parmesan breadcrumbs over the pasta and chicken, drizzle with the remaining oil and return to the centre rack and grill for 3 to 4 minutes, until nicely browned and crisp. Leave to settle for about 5 minutes before serving warm, directly from the pan.
