Place the chicken in a medium bowl. Sprinkle 2 teaspoons cornstarch over the top, then with a spoon, stir to evenly coat the chicken in the cornstarch.
In a separate bowl or liquid measuring cup, stir together the soy sauce, bourbon, maple syrup, brown sugar, vinegar, garlic, ginger, black pepper, and remaining 2 teaspoons cornstarch.
In a large, deep skillet, heat the oil over medium high heat on the stove top. Once the oil is hot and shimmering, carefully add the chicken, breaking apart any pieces that stick together. Brown on all sides, stirring every so often, until the chicken is golden and cooked through.
Add the bourbon sauce. Cooking, stirring often, until the sauce is glossy and thickened, 2 to 4 minutes (you'll still have plenty of extra sauce, ideal for spooning over the rice). Stir in the green onions. Serve hot over rice, with additional green onions sprinkled on top.