Slow Cooker Mongolian Beef & Pineapple

Name: Slow Cooker Mongolian Beef & Pineapple
Cuisine: Asian
Ingredients: ⅓ cup cornstarch; 1 tsp baking soda (optional); ¼ tsp salt; ¼ tsp black pepper; 2 tsp cooking oil; 1 ½ lb flank steak (cut across the grain into thin strips); ½ cup low sodium soy sauce; ⅔ cup low sodium beef broth; ⅓ cup brown sugar (packed); 2 Tbsp hoisin sauce; 1 Tbsp Thai sweet red chili sauce; ¼ to ½ tsp red pepper chili flakes ((to desired spice level)); 2 cloves garlic (minced); 1 tsp fresh ginger (minced); ½ cup matchstick carrots; 1 cup pineapple chunks/tidbits; ¼ cup (+) pineapple juice ((reserved from canned pineapple)); cooked rice (for serving); 2 green onions (sliced thinly, for garnish (optional)); Sesame seeds (for garnish (optional))