Place a cast iron or non-stick skillet over medium heat. Add olive oil and onions and saut́e for 2-3 minutes until softened. Transfer to a large bowl.
Add remaining ingredient to the bowl with the onions and stir with a fork or spatula to thoroughly combine.
Using your hands, form the mixture into 4 even sized patties.
Add enough avocado oil to lightly cover the bottom of the same pan used for the onions. Place skillet over medium heat.
Once hot, add the patties to the skillet and cook for 3-4 minutes on each side until browned. Add more oil to the skillet if necessary to keep from sticking.
A minute before patties are done, lay a slice of cheddar on top of each one, cover the skillet with a lid until melted.
Serve patties in a pita pocket, on a bun or over top a salad.
Notes
*You can use all (3 tablespoons) dijon mustard, all hummus or a mixture of both as stated in the recipe. Adjust to your preference or what you have on hand. You will need a total of about 3 tablespoons though to hold/bind the tuna mixture together.