Make the basil avocado mayo. In a small bowl using a fork, combine mashed avocados, mayonnaise, lemon juice, basil, salt, and cayenne.
If your bread isn't sliced, slice it into 3/8" thick slices. At this time slice the mushrooms as well.
Oil (Important!) and turn on your panini maker or waffle maker (we used a waffle maker).
Spread the basil avocado mayo on the slices of bread.
Next, add a layer of salmon to the bread.
Lastly, add a layer of mushrooms.
Place the tartine in your oiled panini maker or waffle maker and close the lid. Be sure you don't smash the tartine though.
Let cook for 5-6 minutes.
Top with fresh capers and enjoy!