With sauce simmering, add sliced chicken. Stir and return to a simmer, then cover and remove from heat. Allow to sit for 10 minutes, covered, then add peas and reserved mushrooms. Stir to combine.
If you don't have a favorite curry powder, I really like this Frontier Curry Powder. It's got lots of flavor but it's not too spicy. ** I really like Red Boat Fish Sauce. It's won lots of awards and is very high quality. I said this in the post but I'll repeat it here. Don't smell it. Take it from me, it stinks. But just a dash adds delicious, authentic Thai flavor that can't be substituted with anything else. If you like things really spicy, add a tablespoon or two of red curry paste to the curry and ginger/lemongrass mixture in the recipe.