Begin by cutting the boneless skinless chicken breasts or tenders into bite-sized pieces, approximately 1 inch each. Place the chicken pieces in a shallow dish and sprinkle them evenly with cornstarch.

In a skillet, heat a tablespoon of olive oil over medium-high heat until shimmering. Add the coated chicken pieces in a single layer and lightly brown them for about 2-3 minutes on each side.

Once browned, transfer the chicken pieces to the slow cooker, spreading them out evenly. Scrape any browned bits from the skillet into the crockpot.

In a mixing bowl, combine the orange marmalade, reduced-sodium soy sauce, white vinegar, sesame oil, ground ginger, minced garlic, and crushed red pepper flakes. Whisk together until smooth.

Carefully pour the prepared sauce over the chicken in the slow cooker, ensuring all pieces are generously coated. Stir gently to incorporate.

Cover the slow cooker and set it to cook on LOW for 2-3 hours or on HIGH for 1.5-2 hours. Stir halfway through cooking.

Once the cooking time is up, spoon the chicken into bowls and garnish with a sprinkle of sesame seeds and chopped scallions.