Slice (if not pre-sliced) and toast the bread to your liking. (When I use soft pre-sliced bread I usually toast it a little more than I do when I use sourdough.) 

Cut the avocado in half. Carefully remove the pit. Remove the avocado meat from the skin and either slice or mash the avocado onto the toast. 

Next, half or quarter the grape tomatoes and lay onto of the avocado. 

Finally, squeeze some fresh lemon juice on top, throw on some fresh herbs, and salt and pepper as pleased.