I am trying to make split pea soup.  The first time I did it the peas softened just fine but the soup was scorched.  I am trying again but at a lower heat, and the peas are refusing to soften.  Ingredients are 1 bag each of split peas, frozen carrots, and frozen onions, plus a small amount of Spike seasoning.  How can I soften the peas without scorching the soup?  Is a slow cooker the best option? 
The reason your split peas are hard is that you added salt or stock to the water before they finished cooking. From your initial post, you say you've added something called "Spike seasoning". I'm guessing that's the culprit. It's probably got salt in it.   You have to cook split peas in just water for at least an hour, then stir to break them down and add any vegetables to flavor the soup. Only after another 30 minutes or so should you add salt to taste.  