Cashew Chicken and Asparagus

Name: Cashew Chicken and Asparagus
Ingredients: ¼ cup seasoned rice vinegar; 2 Tbsp. oyster sauce; 3 Tbsp. soy sauce, divided; 2 Tbsp. sugar; 2 tsp. plus 1 Tbsp. cornstarch; 2 tsp. toasted sesame oil; 1 lb. skinless, boneless chicken breasts, halved crosswise, sliced against the grain into ½-thick strips (about the size of french fries); 4 Tbsp. vegetable oil, divided; ⅔ cup roasted cashews, preferably unsalted; 2 bunches asparagus, woody ends trimmed, tips reserved, sliced on a diagonal into ¾-long pieces; 1 bunch scallions, finely chopped; 6 garlic cloves, finely chopped; Kosher salt (optional); Steamed white rice (for serving; optional)