Spread 1 tbsp mayonnaise on 2 slices of bread, set mayo-side down on a baking sheet or board (to capture prep mess).
Spread mashed avocado on bread slices on baking sheet. Top with sliced tomatoes, camembert and basil. Cover with the remaining 2 bread slices. Spread remaining 1 tbsp mayonnaise on panini top.
Grill for about 4 minutes until browned.
Notes
You can easily do this recipe without a panini grill, using a skillet or griddle. Just add a bit of butter to the pan before starting, grill for about 3 minutes, flip over, and grill for another 3 minutes until browned.