Heat large skillet over medium heat, then add 1 tablespoon butter. When foam subsides, add shrimp and cook until they just turn pink. Remove from pan and reserve. Add remaining 1 tablespoon butter to pan. When it melts, add onions and stir; cook 5 minutes until softened. Sprinkle 1 teaspoon salt, 1/2 teaspoon pepper, curry powder, garlic and ginger over the onions, reduce heat to low, and cook gently 5 minutes until onions are softened and translucent. Add red pepper and chayote and cook 5 minutes. Add about 2/3 of the coconut milk and simmer, uncovered, 10 minutes to bring flavors together. Add shrimp back to skillet along with scallions, cilantro leaves and lime juice. Taste and adjust seasoning adding more pepper if necessary, adding more coconut milk if desired for a soupier consistency. Serve over rice.