In a medium mixing bowl, whisk together 1/3 cup lite soy sauce (or tamari), 1/4 cup packed brown sugar, 2 tablespoons olive oil, 1 tablespoon freshly grated ginger, juice of 1 lime, 3 minced garlic cloves, and 1 teaspoon Sriracha until the sugar dissolves and the mixture is smooth.
Place 2 1/2 pounds boneless chicken thighs into a large resealable freezer bag. Pour the marinade over the chicken, press out excess air, seal the bag, and place it in a bowl to catch any leaks.
Refrigerate the bag and marinate the chicken for at least 1 hour or up to overnight for more flavor.
When ready to cook, preheat your grill to high heat and brush the grates lightly with oil to prevent sticking. Remove the chicken from the bag and discard the marinade.
Place the chicken on the hot grill and cook 5 to 7 minutes per side, flipping once, until the outside is browned and an instant-read thermometer inserted into the thickest part registers 165°F (74°C).
Transfer the cooked chicken to a platter, season with salt and pepper to taste, and garnish with sliced green onions and chopped cilantro. Serve warm.