Begin by cutting the avocado into medium sized chunks. Place in a small bowl with the lime juice, salt, pepper and cayenne. Stir to combine, gently breaking up the avocado but still leaving it chunky.
In a small bowl combine the mayo, mustard and hot sauce. Whisk together.
To assemble the sandwich liberally slather one side of each slice of bread with the spicy mayo. Lay the slices flat, mustard mayo side facing up and place two slices of cheese on one slice of bread, followed by the avocado mixture. Next add the sliced onions followed by the greens. Top with the other slice of bread.
Cut in half and serve.
Recipe Courtesy of Megan Mitchell