Place chicken pieces in strainer and squeeze lemon evenly over the meat. Wash chicken off with cold water, and pat with paper towels.
Move chicken to a medium-sized bowl and season with salt and pepper. Then add garlic, ginger, thyme, onion, soy sauce, and oyster sauce.
In a deep pot over medium heat, add stock, carrots, pumpkin, tomato, tomato paste, and potatoes. Once veggies begin to soften, add the chicken. Let simmer for about 30 minutes, then add the corn and scallion.
Cook for another 15 minutes, stirring occasionally.
Finish with cilantro, and add additional salt to taste.