Rinse the upo and peel the skin off. Cut them into bite-sized pieces, about ¼-inch thick. Set it aside.If the upo is young and the seeds are tender, you can leave them in; however, for more mature upo with harder seeds, it's best to remove them.
Prepare the sauce by combining oyster sauce, soy sauce, sugar, and ½ cup of water in a bowl. Set aside.
Heat your wok over medium-high heat, then add a small amount of oil to coat the bottom. Lightly season the shrimp with salt, then quickly sear them just until they turn pink, about 2 minutes. Transfer to a plate and set aside.PRO TIP: To achieve a nice crust on the shrimp without overcooking them, make sure to add them to a very hot pan. This quick sear locks in flavors and creates a deliciously crispy exterior while keeping the inside tender and juicy.
Add a bit more oil if needed, and sauté the garlic and onions over medium heat until they soften, about 2 minutes. Add the tomatoes and cook until they soften and caramelize, about 5 minutes.PRO TIP: Caramelize your aromatics, especially the tomatoes, to create a rich and flavorful base for your ginisa. Take your time and don't rush this step.
If using, add the sliced chili peppers and sauté for about a minute to bring out their flavor and reduce their spiciness.
Add the upo and the prepared sauce. Sauté for 3-5 minutes, constantly tossing, until desired tenderness. Adjust seasoning with salt and pepper to taste. As the upo cooks, it will release more water, which may thin the sauce.
Return the cooked shrimp to the pan and mix gently to combine. Turn off the heat.
Serve your Ginisang Upo with a side of steamed rice, and enjoy!
Notes
Upo: Also known as bottle gourd, it is a long, green vegetable with a mild and slightly sweet taste. Zucchini or chayote, both from the gourd family, make suitable substitutes.
Shrimp: It cooks quickly and complements the mild flavor of the upo well. You can also use chicken, pork, tofu, or fish.