Combine the lentils with 1 ½ cups water in a saucepan over high heat. Once it boils, turn down to a simmer and cook uncovered until the water is almost all the way evaporated and the lentils are tender, about 20 - 30 minutes.
Heat the oil in a large skillet or wok over medium heat. Sauté the green onions until they soften, about 2 - 3 minutes.
Add the shrimp, lentils, ginger, and red pepper to the pan. Cook while stirring until the shrimp is pink and cooked all the way through, about 4 - 5 minutes.
Stir in the soy sauce and sesame oil and let cook down for a minute or two. Sprinkle on the cilantro, spoon into lettuce cups, and serve.