Scoop half the avocado into a bowl and lightly mash with a fork. Add the chipotles, sun-dried tomatoes, and lemon juice and mix until combined. Stir in the tuna, basil, and oregano. Season with pepper.
Layer the butter lettuce onto the pitas and stuff with the tuna salad. Slice the remaining avocado half and add to the sandwiches. Add the arugula and microgreens and serve.
