Place coconut milk, pineapple, garlic, ginger, garam masala, and curry powder into the Vitamix container and secure the lid. Start the blender on its lowest speed, then quickly increase to its highest speed. Blend for 45 seconds. While the sauce is processing, preheat a large skillet over medium-high heat. Once hot, add oil and heat until shimmering. Add shrimp and cook halfway through, then add peas and spring onions. Cook for 2 minutes. Pour in the blended sauce and bring contents of the pan to a simmer, cooking for 15-20 minutes. Add the cornstarch and water slurry to the skillet. Whisk in and simmer for an additional 5 minutes. Serve over basmati rice.