To prep the mushrooms, just give them a quick rinse and simply slice each in half. To prep canned mushrooms, just drain and rinse, then slice each in half.
Gather up the remaining ingredients to get them ready.
Heat the oil in a non stick pan, when hot, add the onion, curry leaves, garlic and cardamom. Stir often and cook until the onion is browning on the edges.
Add the mushrooms and cook, stirring often until they are just starting to brown, about 3-5 minutes depending on using fresh or canned, canned will brown sooner than fresh.
Sprinkle in the turmeric, curry powder, and chili powder and let the mushrooms cook for a few more minutes.
Add the tomato sauce and stir in, taste and season with salt as desired. Cook for just a few minutes until the mushrooms are nicely browned.
Add the coconut milk and reduce heat to a low simmer and cook until you have a thicken the curry sauce to your liking.
Serve over toast or with rice.