Slow Cooker Mongolian Beef & Pineapple

Name: Slow Cooker Mongolian Beef & Pineapple
Cuisine: Asian
Ingredients: 1/3 cup cornstarch; 1 tsp baking soda, optional; 1/4 tsp salt; 1/4 tsp black pepper; 2 tsp cooking oil; 1 1/2 lb flank steak, cut across the grain into thin strips; 1/2 cup low sodium soy sauce; 2/3 cup low sodium beef broth; 1/3 cup brown sugar, packed; 2 Tbsp hoisin sauce; 1 Tbsp Thai sweet red chili sauce; 1/4 to 1/2 tsp red pepper chili flakes (to desired spice level); 2 cloves garlic, minced; 1 tsp fresh ginger, minced; 1/2 cup matchstick carrots; 1 cup pineapple chunks/tidbits; 1/4 cup + pineapple juice (reserved from canned pineapple); cooked rice, for serving; 2 green onions, sliced thinly, for garnish (optional); Sesame seeds, for garnish (optional)