In this case I've used chunks of leftover lamb (cooked sous vide by ewilhelm for our potluck) but you could also use chicken, fish, shrimp, tofu, or whatever you're excited about. I'm going to start making this sauce by the bucketload, and adding whatever previously-cooked meat we have on hand. The important part is using pre-cooked meat (or seafood that cooks very quickly) for maximum speed and tastiness.
Step 1: Onions and curry
Add 2 Tablespoons of your favorite curry powder, and stir until thoroughly mixed. If it starts to stick or burn, add more fat.
Using a microplane grater, grate in two cloves of garlic. Stir in with the rest of the onion/curry/oil paste.
Step 2: Add coconut milk and meat
Since the lamb is already cooked, you're just simmering long enough to dry the curry a bit more, and make sure all the amazing flavors penetrate the meat. This should take around 5 minutes.
If you like, this is the time to add golden raisins (sultanas), cashews, cilantro, or any other interesting chunks you'd like in your curry.