Rinse and drain the chickpeas, then pat them thoroughly dry with a paper towel.
In a small bowl, toss the dried chickpeas with garlic powder and a pinch of the salt and pepper.
Heat the olive oil in a non-stick skillet over medium-high heat and add the chickpeas, sautéing for 5-7 minutes until golden and crispy.
While the chickpeas cook, whisk together the lemon juice, Dijon mustard, and the remaining salt and pepper in a small jar or bowl to create the dressing.
In a large salad bowl, combine the arugula, diced cucumber, and thinly sliced red onion.
Drain the tuna and flake it into the bowl with the greens.
Add the warm, crispy chickpeas to the salad and drizzle the lemon-dijon dressing over the top.
Gently toss everything together and finish with the sliced avocado before serving.