In a large mixing bowl, whisk together the sweet chili sauce, soy sauce, fish sauce, lime juice, minced garlic, grated ginger, minced lemongrass, and vegetable oil. This fragrant mixture forms your sticky Thai marinade.

Pat the chicken drumsticks dry with paper towels to ensure crispy skin, then add them to the marinade. Toss well to coat every piece, cover the bowl, and let marinate at room temperature for 15 minutes while the oven preheats.

Preheat your oven to 400°F (200°C). Line a rimmed baking sheet with aluminum foil and place a wire baking rack on top, spraying the rack lightly with non-stick cooking spray to prevent sticking.

Arrange the marinated drumsticks on the prepared rack, shaking off excess marinade into the bowl to reserve for later. Bake the chicken in the preheated oven for 25 minutes, until the skin begins to shrink and lightly brown.

While the chicken bakes, pour the reserved marinade into a small saucepan. Simmer over medium heat for 3 to 5 minutes until it reduces and thickens into a syrupy glaze.

Remove the chicken from the oven and brush each drumstick generously with the thickened glaze. Return to the oven and bake for an additional 15 to 20 minutes, until the internal temperature reaches 165°F (74°C) and the glaze is sticky and caramelized.

Let the chicken rest for 5 minutes before serving so the juices can redistribute. Garnish with freshly chopped cilantro and serve alongside steamed rice for a delicious, homestyle Thai meal.