The key feature of the new fish sandwich is a patty made with chunks of wild-caught salmon, diced cheddar cheese, red and yellow bell peppers, and a paella spice mix. Accompanying the patty is salad mix, mayo, and a multi-grain topped bun.
While they don't mention what's in the paella spice mix, a typical paella recipe tends to include saffron, garlic, parsley, and onion.
The sandwich seems to come in response to customer complaints of a lack of newness and excitement on the menu (which is funny to me because McDonald's Singapore puts out a lot more limited-time items than we get here in the U.S.). They illustrate the concept in a TV spot:
Photo via McDonald's Singapore.