In a food processor, puree 1/2 red onion, serrano chile, cashews, yogurt, ginger, garlic and lime juice until smooth. Remove lid and add the Kashmiri chili powder, fenugreek leaves, salt, cumin, garam masala, coriander and turmeric. Pulse several times until blended well.
In a large bowl add the chicken, marinade and mix well. Cover with plastic wrap and refrigerate to marinate for 30 minutes minimum, 4 hours maximum.
Thread marinated chicken, peppers and onions on skewers, alternating between each (see image). Spray both sides of kebabs with cooking spray. Place a wire rack over a lined baking sheet. Spray with cooking spray to avoid sticking and lay kebabs on top.
Preheat oven to 400°F. Cook for 15 minutes. Turn oven broiler on and broil skewers for 5 minutes, or until slightly charred and cooked through. (See Note 1 for grilling instructionsTo )
Remove from oven and serve with chutney, lime slices, red onion and cilantro sprigs. Wonderful with warm naan as well.