Serve as a condiment with lamb or chicken. To shorten preparation time, substitute canned chickpeas for dried, and start at step 2.
Pick over dried chickpeas. Rinse and soak overnight in cold water with 1 teaspoon salt. Drain and rinse. Place chickpeas in a medium saucepan, and cover by several inches with fresh water. Bring to a boil, and skim off any foam. Turn heat down to medium, and simmer until tender, 35 to 45 minutes. Ten minutes before chickpeas are done, add 3/4 teaspoon salt. Remove from heat; let cool in cooking liquid for about 1 hour.
If using cumin seeds, toast in a dry pan over medium-low heat until they release their aroma, about 2 minutes. Let cool and grind to a powder in a spice grinder. Set aside.
Chop together 1/2 teaspoon salt, garlic, and 1/2 teaspoon olive oil to form a paste. Add chiles; chop to combine. Transfer to a small bowl, and add remaining oil.
Drain soaked chickpeas. (If using canned chickpeas, rinse.) Combine with 1 teaspoon chile mixture or to taste. Add olives, cumin, lemon juice, and salt and pepper to taste. Refrigerate until ready to serve. The salsa can be made a day ahead (return to room temperature before serving).
Just before serving, coarsely chop arugula, and toss with salsa.