First, make the chukka masala. Place a dry skillet over medium heat. Add the coriander seeds, cumin seeds, fennel seeds, peppercorns, cloves, cardamom, cinnamon stick, and dried red chilies. Toast, stirring often, for 2-3 minutes until fragrant. Add the shredded coconut, cashews, and one sprig of curry leaves. Continue toasting for another minute until the coconut is golden and the leaves are crisp. Remove from heat and let cool completely.
Once cool, transfer the toasted spice mixture to a spice grinder or high-powered blender. Grind into a fine powder. Set aside.
Heat the sesame oil in a large pan or skillet over medium-high heat. Add the remaining sprig of curry leaves and the chopped shallots. Sauté for 5-6 minutes, until the shallots soften and turn light golden brown.
Stir in the ginger-garlic paste and cook for one minute until fragrant. Add the chicken pieces, salt, and turmeric powder. Sauté for 3-4 minutes, stirring to coat the chicken, until it is no longer pink on the outside.
Sprinkle all of the prepared chukka masala powder over the chicken. Stir well to ensure every piece is coated. Reduce the heat to medium, cover the pan, and cook for 10-12 minutes, stirring occasionally.
Uncover the pan. The chicken should be cooked through and tender. If it appears dry during cooking, you can add a splash (about ¼ cup) of hot water. Check for doneness with a meat thermometer; it should read 165°F (74°C) at the thickest part.
Increase the heat to medium-high and cook for another 2-3 minutes, stirring constantly, to evaporate any excess moisture. The masala should cling tightly to the chicken, creating a dry, thick coating.
Remove the pan from the heat. Stir in the lemon juice. Taste and adjust salt if needed. Garnish with chopped cilantro if you like, and serve immediately.