COAT THE CHICKEN: Place the uniform 1-inch chicken pieces into a large zip-top bag along with the cornstarch. Seal tightly and shake vigorously until every piece is evenly coated.
SEAR FOR FLAVOR: Heat the extra virgin olive oil in a large skillet over medium-high heat. Add the coated chicken in a single layer and sear for 2-3 minutes per side until a light golden crust forms. Transfer the seared chicken directly into your slow cooker.
WHISK THE GLAZE: In a medium bowl, combine the low-sodium soy sauce, hoisin sauce, brown sugar, rice vinegar, sesame oil, minced garlic, grated ginger, and optional red pepper flakes. Whisk until the sugar is fully dissolved.
SLOW COOK: Pour the mixed glaze directly over the chicken in the slow cooker. Toss gently to coat. Cover and cook on LOW for 3 to 4 hours (or on HIGH for 1.5 to 2 hours) until the chicken is tender and cooked through.
ADD THE CRUNCH: Approximately 15-20 minutes before serving, stir the whole roasted cashews into the slow cooker. Replace the lid to let them warm through and become beautifully glossy.
SERVE AND GARNISH: Ladle the sticky cashew chicken over warm brown rice, jasmine rice, or quinoa. Scatter the sliced green onions and fresh cilantro leaves over the top immediately before serving.