Chop some onions into rings.
Boil plenty of water in a wide enough pan for the sausages to fit in.
Grate the cheese if necessary.
Heat up an oven if you want your tortilla wraps crispy.
Take the water off the boil and heat up your sausages in the hot water. Make sure their skin doesn't crack. Heat up some oil + butter in a broad pan and add your sliced onions to it. Once they start getting a nice brown colour, turn down the heat and let them caramelise / cook slowly. Don't stir too often; add a little water if necessary. If you want, you can heat up your wraps in the same pan, or on a plate above the boiled water, or in the oven. If the sausages are through and through warm, you can either lightly brown them in the pan, or put them straightaway on the wraps with the onions, lettuce mix, grated cheese and various sausages.
Serve open (as shown on the picture), or wrapped up (sticking a toothpick through it to hold it in place).