Cut chicken breasts into cubes and place in a large bowl.
Heat skillet to medium and add ghee or butter. Add onions, garlic, ginger, green peppers, and jalapeno and sauté, about one minute. Add spinach leaves and continue to sauté until leaves wilt.
Transfer skillet contents to a blender or food processor. Add lemon juice, lemon zest, cilantro, cashew butter, spices, and water. Puree until smooth. Remove about ¼ cup of puree to make finishing sauce. Pour marinade mixture over cubed chicken, cover, and refrigerate for 6-8 hours.
Soak bamboo skewers in water for a few minutes and add 4-5 pieces of chicken per skewer. Dab cooking oil over chicken and grill covered on each side, about 4-5 minutes.
Combine ingredients for the extra sauce. Add enough water to make sauce spreadable, about 2 tablespoons. Adjust seasoning to taste. Brush sauce over cooked chicken.