It’s best to use prawns with heads because the prawn fat not only gives the broth a beautiful color but also makes it much more flavorful. When peeling prawns, carefully extract the fat into a bowl and discard heads, shells and veins. Slice prawns on bias or crush into chunky pieces. Place in the bowl with the prawn fat along with fresh chili, ground pepper and fish sauce. Toss ingredients together and set aside to marinate while you prepare the rest of the ingredients.
There are different ways of cutting the opo squash for soup. I’ve seen it cut into cubes as well as thin semi-circular disks, but I prefer the matchsticks because they cook up in a flash and are much easier to eat. I like to eat the skin on most of my fruits and vegetables, especially when it has not been waxed. The thin skin of the opo squash adds a nice taste and crunch, but you can peel it off if you wish.
Place soup pot over high heat and drizzle with a bit of olive oil. When oil is hot, throw in shallots and red chili powder. Toss until fragrant and put the prawns in. Stir quickly and as soon as prawns turn slightly pink, pour in the water. I usually don’t measure the water, instead, I just eye it based on the size of the squash and how watery I want the soup. Bring water to a roaring boil and dump the squash into the pot. Always cook and reheat vegetables or vegetable soup uncovered in order to retain the freshness and beautiful green color. There is nothing worse than mushy, olive-colored vegetables! Give it a stir and adjust seasoning. The soup is done when the opo turns a bit translucent. I like a bite to my opo, so I usually just take it off the burner as soon as the water starts to boil again. The opo will continue to cook in the broth even after you take it off the heat, so you don’t want to overcook it and have mush…unless you desire that texture. Immediately after taking it off the heat, add scallions and cilantro and give it a quick stir. You can eat this light and delicate soup alone or on top of a bit of jasmine rice.