Cook the rice: Combine jasmine rice and 4 cups of water in a saucepan. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes. Remove from heat and let stand, covered, for 10 minutes. Fluff with a fork.
Prepare the chicken: In a bowl, toss the chicken pieces with 1/2 cup cornstarch, salt, and pepper until coated.
Cook the chicken: Heat 2 tablespoons of vegetable oil in a large skillet or wok over medium-high heat. Add chicken in a single layer (work in batches if necessary) and cook until golden brown and cooked through, about 5-7 minutes. Remove chicken and set aside.
Make the sauce: In the same skillet, add the remaining 1 tablespoon of oil. Add orange juice, sugar, soy sauce, rice vinegar, ginger, garlic, sesame oil, and sriracha (if using). Bring the mixture to a simmer.
Thicken the sauce: Whisk the cornstarch slurry into the simmering sauce. Cook, stirring constantly, until the sauce thickens and becomes glossy, about 1-2 minutes.
Glaze the chicken: Return the cooked chicken to the skillet. Toss gently to coat all pieces thoroughly with the sticky orange sauce.
Cook the vegetables: While the chicken is glazing, steam or lightly stir-fry the mixed vegetables until tender-crisp.
Assemble the bowls: Divide the cooked rice among serving bowls. Top with the glazed orange chicken and serve the steamed vegetables alongside or mixed in.
Notes
For extra crispy chicken, dredge the coated pieces in flour after the cornstarch, or briefly fry them twice.
To achieve maximum stickiness, allow the sauce to reduce slightly before adding the chicken back in.
Use fresh orange zest in the sauce for a brighter flavor.