In a large mixing bowl, whisk together the lemon juice, 1½ teaspoons of salt and crushed cardamom seeds. Slash the chicken thighs two or three times through to the bone, then add them to the lemony brine, mixing well to ensure it gets in all of the slashes. Set aside to brine for 30 minutes.
Next, make the spice paste. Whisk together the garam masala, turmeric, miso, garlic, ginger, black pepper, lemon zest and vinegar. Pour the paste over the brined chicken, mixing well with your hands to ensure it gets deep into the grooves. Put into the refrigerator to marinate for 2 hours (or leave on the counter for 1 hour).
Preheat the oven to 400 F. Spread out the fennel, onion, and peppers in a large roasting pan. Drizzle with oil, sprinkle with salt and the crushed cumin seeds and toss all together. Place the marinated chicken on top, spooning out all the spice paste to cover it completely.
Roast for 45-50 minutes until cooked through, charred in spots, and tender - cover with foil if browning too quickly. Drizzle with more olive oil, a squeeze of lemon, and top with the chopped dill to serve.