Whisk together the mayo and the sriracha sauce. BOOM! Sriracha mayo!
Spread the mayo on both slices of bread, then layer on the tomato, arugula, and avocado. Close up your sandwich and use the palms of your hands to gently press it as flat as you can without making the goods fly out.
Heat the oil in a skillet on medium heat, and drop in your sandwich into the pan. Cook for 4 minutes, flip with a spatula, and cook for 3 minutes more. You can use the spatula to gently flatten the sandwich a bit more while it’s in the pan. Just don’t press hard – you want it to be nice and compact, but you don’t want it sliding apart or pushing the tomato out.
If you like a toastier sandwich, you can do another minute per side at the end (that’s two extra flips).
Flip the sandwich onto a cutting board, cut it in half, and serve.
Pressing this sandwich is key. If you don’t press it before you throw it in the pan, it’s almost guaranteed to fall apart when you flip it. When you press, apply even pressure, and use your free hand to kind of nudge anything that tries to escape back in. Nice try, sneaky piece of tomato!