To make the mayo, mix all ingredients in a bowl and season with salt. Preheat the broiler to high. Working on a sheet pan, spread the outside of each piece of bread lightly with butter. Spread the inside with spicy mayo. Place the cheese slices over the mayo, then add the tomatoes – cut side up. Broil 2-4 minutes, until the cheese is bubbling up and the tomatoes begin to char. Watch closely. Layer the sun-dried tomatoes, pickles, pepperoncini, sprouts, avocado, red onion, and jalapeños. Add the top piece of bread, cheese facing down. Slice and enjoy while warm with lots of extra mayo.