Toss the rice with the vinegar. In a large nonstick skillet, heat the oil over medium-high heat. Season the eggs with salt and pepper and pour into the pan, swirling to cover the bottom. Pull the cooked eggs from the edge toward the center, swirling, and cook until set, 30 seconds. Slide onto a plate, flip back into the pan and cook for 10 seconds; transfer to a work surface. Cut into inch-wide strips.
Add the Spam to the skillet and cook for 5 minutes. Whisk together the sugar, oyster sauce and soy sauce. Pour over the meat and cook for 1 minute. Transfer the meat to a work surface and brush some of the remaining glaze over the nori.
Arrange a bowl of water and the rice near the work surface. Line the reserved Spam can with plastic wrap. Press 1/3 cup rice into the can and layer with an egg strip and a slice of meat. Lift the filling out of the can and set crosswise in the center of a sheet of nori; fold the ends over, dampening the edges to seal. Repeat with the remaining ingredients. Serve whole or sliced crosswise into 3/4-inch pieces.