Set heat to medium. To a dutch oven, add oil, onion, garlic, and ginger; cook, stirring often, until mixture is fragrant and onion softens, 2 to 3 minutes. Stir in rice, salt, and pepper. Add stock, and bring to a boil over medium-high; immediately reduce to a simmer over medium-low, and cook, uncovered and stirring occasionally, until rice is just tender, 17 to 20 minutes.
Stir shredded chicken back into rice. If porridge becomes too thick, add additional stock, ½ cup at a time, as needed to reach desired consistency. Stir in fish sauce, and garnish with fried shallots and sliced scallions. Serve with lemon wedges.
