How to Make It
Make the sweet chili sauce: Stir together the ketchup, vinegar, soy sauce, and sugar in a small pot. Bring to a simmer over medium, stirring constantly, until sugar dissolves, about 1 minute. Whisk cornstarch into 1/2 cup cold water; add to the pot and bring to a boil, stirring constantly, until mixture thickens, about 2 minutes. Remove from heat, and set aside.
Make the oyster omelet: Shuck oysters, reserving any juice in shells. If the oysters are large, cut them in half. Whisk the sweet potato starch into 1/4 cup water in a medium bowl. Stir in salt, oysters, and any oyster juice.
Heat oil in a medium nonstick skillet over high. Let it get quite hot, then add the oyster mixture. Reduce heat, and let mixture set into a thick, translucent pancake with a jelly-like consistency, about 4 minutes. Stir in spinach and scallions.
Break eggs into a bowl, stir them with a fork, then add them to the skillet. Allow to just set, then flip the omelet as gently as you can (don’t worry if it breaks). Cook until bottom is just set but eggs are still a little runny, about 1 minute. Flip the omelet onto a plate, and serve with the sweet chili sauce. (It might not be pretty, but you’re going to top it with sweet chili sauce, so it doesn’t matter.)