Recipe notes:
Romaine lettuce is what I had so it's what's in it. I cannot personally vouch for the results with other lettuce varieties, but I can't see it working especially badly with any variety. Your mileage may vary.
I've said "tinned mushrooms" because it's what I had and used and this is an honest recipe, but obviously use fresh mushrooms if you prefer.
Maggi liquid seasoning is a solid staple for South Asian cooking; it's made from wheat, but it's functionally just a vehicle for tasty, tasty MSG. I'm told there are other brands, but Maggi is the one you tend to see in supermarket World Food aisles. If you don't have it, soy sauce (especially the dark variety) is a decent substitute.