Rinse the zucchini and halve lengthwise.
Heat a non-stick grill pan. Place zucchini halves cut sides down on pan and grill over low heat until tender and browned in spots, 10-12 minutes. Season with salt and pepper and let cool for 10-12 minutes.
Meanwhile, rinse tomatoes, wipe dry, cut out stems and cut into slices.
Remove tough stems from arugula, then rinse and spin dry.
Brush the tahini over the cooled zucchini halves. Top with arugula and tomato slices and serve, sprinkled with sea salt.