Set noodles in a bowl; cover with hot tap water and let sit for 10 minutes. Drain noodles and cover with more hot tap water and let sit for 5 minutes longer. Drain noodles again and cut them into roughly 4-inch lengths. (Alternately, you can cover dried noodles with boiling water and drain and cut after soaking 5 minutes.) Toss cooked noodles with sesame oil and fish sauce.
Heat 1 1/2 tablespoons vegetable oil in a 12-inch skillet set over medium heat. Add half the shrimp and saute for 2 to 3 minutes or until just cooked through. Add half the green onion and half the garlic and cook, stirring constantly for 1 minute. Season lightly with salt, pepper, and Essence, and transfer to a small bowl. Repeat with the remaining oil, green onion, garlic, and shrimp.
Select smallest whole cupped leaves or tear larger leaves and stack together to form a small cup. Arrange cups side by side on a serving platter. Add a small bed of noodles and a few shrimp to each lettuce cup. Drizzle with Nuoc Cham. Garnish each with a thin slice of jalapeno, if desired. Serve immediately.