In a small bowl, combine tahini, water, lemon juice, sea salt and garlic powder. Mix until combined. If it's too thick, add a touch more water to desired consistency.
If bread is frozen, let thaw 10 minutes before assembling sammie. Using a fork, flatten falafel before adding to sammie.
Place flattened falafel onto sammie. Top with pickled onions, tomatoes, drizzle with tahini dressing and some parsley.