Heat the vegetable oil in a large skillet or wok over medium-high heat. Add the minced lemongrass, garlic, and ginger, and sauté for about 2 minutes until fragrant.
Add the sliced chicken thighs to the skillet and cook for 5-7 minutes, stirring frequently, until the chicken is browned and cooked through.
Stir in the sliced red bell pepper and snap peas, cooking for an additional 3-4 minutes until the vegetables are tender-crisp.
In a small bowl, whisk together the soy sauce, fish sauce, brown sugar, and lime juice. Pour this mixture over the chicken and vegetables, stirring to combine. Cook for another 2 minutes to heat through.
Remove from heat and garnish with fresh cilantro. Serve over cooked jasmine rice.