You can leave your shrimp shells on or peel them if you want, leaving the tail and head on. Then clean and devein your shrimp (use heavy salt to wash if fishy).
Make sure all the water has been drained, then season with turmeric, red chili powder, and salt. Massage into the shrimp carefully or toss in the bowl to cover all the shrimp.
Heat your pan on high heat, pour in your oil and let it heat up. Then toss in your shrimp and fry for just a minute until nice and golden/orange, flipping halfway through. Do not overcook, and fry in 2 batches if needed so you don't overcrowd the pan and can get a nice fry.
Take out all the shrimp and put it in a wide bowl so they don't steam too much, and turn the heat down to med-high
Add in your sliced onions. Occasionally stir and fry until it starts to brown. Then add in all your whole spices. Stir and fry for a minute
Pour in your onion, ginger, and garlic paste, fry for a few minutes until the raw smells are gone, stirring constantly and adding a splash of water to keep the bottom from burning if needed.
Add in your diced tomatoes, and ground spices. Stir and fry until the oils come out.
Then add in about a 1/4 cup of water, stir constantly and reduce until the oils come out, fry for a minute, then add in more water and repeat this step 3-4 times. The longer you go the better it will taste.
Once your curry base is good to go, add in your salt, sugar, and a half cup of water and stir
Slide in all your cooked shrimp carefully into the gravy. and let it simmer on medium medium-low heat for 5 minutes. Adding in your split green chilis halfway through.
Add in a dash of gorom mosholla/garam masala (optional), taste and adjust salt if needed, then take it off the heat.
Serve hot with lime wedges on the side, and enjoy!