To make peanut sauce, heat 2 tablespoons of oil in a saucepan. Add onion and garlic and fry gently until golden.
Stir in chili powder, Curry Powder, water, peanut butter and brown sugar. Bring to a boil; simmer gently until thickened. Stir in soy sauce and lemon juice, then salt and pepper. Turn mixture into a serving dish.
Preheat broiler. Grease a broiler pan. Trim and cut meat in 1/2" cubes. Thread (not too tightly) onto 8 bamboo skewers, leaving a space at each end for holding. Cover ends with small pieces of foil to prevent burning. Place skewers in greased broiler pan. Brush with remaining 1 tablespoon oil. Cook under preheated broiler 10-15 minutes until golden and cooked through. Turn and brush frequently with oil during cooking. Garnish with lemon pieces and cilantro sprigs, if desired, and serve hot with peanut sauce.