Charcoal, a charcoal chimney, eight 14-inch metal skewers and a spice grinder or mortar and pestle
Make the marinade: Toast the coriander seeds in a small skillet over medium-high heat until fragrant, 2 to 3 minutes. Add the garam masala, paprika, turmeric, cayenne pepper and cinnamon and warm through to make fragrant, about 1 minute. Pour everything into a spice grinder and process until fine. (Alternatively, crush the spices with a mortar and pestle.)
Place the guajillo chiles in a bowl, cover with hot water and let soak for 10 minutes. Drain the chiles and finely chop. Combine the spices with the chiles, yogurt, lemon juice, garlic, ginger and salt in a in a large bowl. Stir well to combine.
Using a meat tenderizer, pound the chicken to a 1/2-inch thickness in between two pieces of plastic wrap. Place the chicken breasts in a large resealable freezer bag. Pour in the marinade and toss to coat well. Refrigerate for at least 1 hour and up to overnight if you have the time.
Heat the charcoal in the charcoal chimney. To closely replicate a traditional tandoor clay oven cooking environment, set two large cast iron skillets (about 12 inches each) over high heat until hot, about 5 minutes.
Remove the chicken from the marinade. Thread a skewer into each chicken piece so the chicken lies flat.
Very carefully remove the skillets from the heat and add a layer of charcoal to one of the skillets. Working in batches, place the skewers over the coals in the skillet so they rest on the rim and the chicken is above the coals. Carefully cover the chicken with the second pan, making sure the skewers don't slip. Cook, turning once, until the chicken is bright red and charred and blackened around the edges, 10 to 12 minutes. Remove the skewers, place them on a plate and repeat with the remaining chicken.
Serve with warm flatbread and raita.
Whole Wheat Garlic Flatbread:
Combine the yogurt, whole wheat flour, all-purpose flour, baking powder, 2 tablespoons chopped parsley and 1/2 teaspoon salt in a food processor and process until the dough is smooth. Wrap the dough in plastic and refrigerate for 30 minutes.
Preheat the grill to medium-high heat.
Divide the dough into 6 equal portions. On a floured surface, using your hands or a rolling pin, flatten each piece of dough into a large oval, about 6-inches in length. Oil the grill grate. In batches, grill the flatbreads until puffy and charred around the edges, 2 to 3 minutes per side. (Alternatively cook in a pizza oven or on a pizza stone for 4 to 5 minutes.) Hold the flatbreads on a plate under a warm towel as you cook the rest.
Combine the butter with the garlic and remaining 1 tablespoon minced parsley and 1 teaspoon salt. Brush the hot flatbreads with the butter mixture.
Cucumber, Mint and Basil Raita:
Combine the yogurt, cucumber, basil, mint, cilantro, agave syrup, cumin, garlic and salt in a food processor and pulse just enough to break down the cucumber and herbs slightly (the raita should still have texture). Do not overmix or the raita will become too runny.
Refrigerate for at least 20 minutes to allow the flavors to come together and for the raita to firm and settle.