Season the shrimp with kosher salt and set aside.
Drizzle a large skillet with olive oil and heat over medium-high heat.
Add the mustard seeds, cinnamon stick, cardamom seeds, green chilies, and cook for 1 minute.
Add the onions and ginger/garlic paste, cook until the onions are translucent.
Stir in the garam masala, turmeric powder, and season with salt.
Stir in the tomato sauce and check for seasoning.
Add the shrimp, cover, and cook for 8-10 minutes.
Add the coconut milk and cook for an additional minute uncovered.
Garnish with cilantro, if desired and enjoy!