Heat 1 1/2 teaspoons oil in a 12-inch nonstick skillet over medium-high heat.
Add meat, brown three minutes, break it up, and cook about three minutes more until done.
Whisk hoisin, soy sauce, sriracha, rice vinegar, and sesame oil in a bowl.
Drain excess liquid, then move meat to one side of the skillet.
Heat remaining oil in the empty side.
Saute green onions and carrots 1 1/2 minutes; add garlic and ginger for 30 seconds.
Add sauce and water chestnuts; toss for 30 seconds.
Serve warm in lettuce leaves with green onions.