In small bowl, stir together paprika, salt, garlic powder, onion powder, pepper and coriander. Set aside.
Drizzle 1 tbsp of the oil on a large baking sheet or shallow roasting pan to coat. Arrange cabbage and carrots in a single layer; sprinkle with salt and pepper.
Using kitchen shears, cut chicken along either side of backbone; remove and discard backbone or reserve in freezer for broth. Turn chicken breast side up; press firmly on breastbone to flatten.
Rub chicken with remaining 1 tbsp oil, sprinkle the spice blend all over, then place on vegetables.
Roast chicken for about 50 minutes or until the internal temperature reaches 165°F. The skin should be golden brown and crispy and juice from the thigh, when pierced with a fork, should run clear. Let rest for 10 minutes.
Place pan in centre of table on top of a wooden cutting board or metal trivets. Finish chicken with a scatter of flaky sea salt. Serve lemon pieces on the side for spritzing
Notes
To crush the coriander seeds, you can use a mortar and pestle, but if you don’t have one, place them on a cutting board and use the flat side of a large knife to crush them.