In a medium bowl, whisk together olive oil, basil, garlic, salt, and pepper. Add chicken thighs to the marinade and mix until the chicken is coated. Cover and refrigerate for 1 to 6 hours, turning occasionally.

In a large saucepan, whisk together chicken broth, orange juice, sugar, butter, tamarind concentrate (paste), orange peel, and ginger. Bring the mixture to a boil over medium-high heat and cook, whisking frequently, until the mixture is reduced to ¾ cup and the glaze coats the back of a metal spoon, 25 to 30 minutes. The glaze should remain at a vigorous boil for the entire time to ensure quick reduction.

Remove from the heat and add several drops sriracha sauce, as well as salt and pepper, to taste.

(The glaze can be made up to 2 days in advance; cover and keep store in the refrigerator. Gently reheat before using.)

Spray the grill with nonstick cooking spray. Heat grill to medium-high heat.

Pour ¼ cup glaze into a small bowl. This will be used for basting. Reserve the rest of the glaze. Transfer the chicken to the grill and discard the marinade. Grill until the chicken is cooked through, about 4 minutes per side, basting with the glaze on both sides of the chicken.

Spoon the reserved glaze over the chicken and serve with rice.