Baking Soda + Lemon Juice
You can substitute baking soda for yeast, but you also need to include an acidic substance with it. A common pairing is lemon juice, but you can also use buttermilk. The baking soda and acid combination is a 1:1 substitute for the yeast. This means if the recipe calls for two teaspoons of yeast, you'll substitute with one teaspoon of baking soda and one teaspoon of acid. You also don't need to let the dough rise or rest like you would with a typical yeast dough.