Pat the chickpeas dry with a paper towel and toss them with half of the avocado oil and a pinch of salt.
Place the chickpeas in an air fryer at 400°F for 12-15 minutes, shaking halfway through, until they are golden and crunchy.
Season the tuna steak on both sides with salt and cracked black pepper.
Heat the remaining avocado oil in a cast-iron skillet over high heat until just smoking.
Sear the tuna for 60-90 seconds per side for a perfect medium-rare, then set aside to rest for 2 minutes before slicing.
In a small jar or bowl, whisk together the tahini, lemon juice, and 1 tablespoon of warm water until the dressing is smooth and creamy.
Combine the arugula, diced cucumber, and halved cherry tomatoes in a large salad bowl.
Slice the tuna against the grain and arrange it over the greens along with the crispy chickpeas.
Drizzle the lemon tahini dressing over the top and enjoy immediately.