Those look so tasty! I'll have to add those to my list of things to buy and try. If you want a better crust, with more of that tasty Maillard reaction browning, use a brush of a spatula to spread that oil around as oil doesn't just keep things from sticking, but is a conductor of heat. Just as cushions will lift and compress themselves around your body, oil lifts and spreads to fill in the uneven surface of what you're cooking. This creates a second, form-fitted cook surface capable of transferring more heat directly to what you are cooking. I'm not sure what temp your slow cooker sears at, but you may find you get better results setting your electric griddle to 325, any higher and you'll start getting charred and burnt spots. While burnt spots aren't desirable on meat, you may want to try adding a bit of char to your onions. A bit of char adds unique and delicious flavor to onions that are not uncommon in Mexican cooking. A lot of salsas will be made with charred tomatoes, onions, and peppers. Good luck and have fun experimenting!