Directions for Shrimp: While squash is roasting, heat oil in a large skillet over medium-high heat. Add shrimp – sear on both sides until shrimp cooked through (look for it to be just barely pink and curled. Be careful not overcook the shrimp at this stage.) About 3-5 minutes. Remove from heat.
Add turmeric and toss until shrimp are ‘yellow’, then transfer to a separate bowl.
In same skillet, cook jalapeño, garlic, ginger, and 1 tablespoon lime juice in 1/2 tablespoon oil in skillet over moderately high heat, stirring, 1 minute. Add water and simmer until water is evaporated and chile mixture is softened, 2 to 4 minutes.
Add half-and-half and tikka masala and simmer 2 minutes. (Remove from heat if squash is not cooked yet.)
When squash is tender, add 2 teaspoons lime juice and shrimp/juices in bowl to masala sauce and simmer until shrimp are just warmed through and sauce is slightly thickened, about 2 minutes.
Slice squash halves. Spoon tikka masala shrimp over squash. Garnish with cilantro and/or jalapeño slices.
(note: I cooked my squash a day ahead of time and placed in fridge. Just reheat halves, covered, for about 5 minutes. Slice and serve.)