Place spinach, red onion, bell pepper, black olives, and a pinch each of salt and pepper in a large mixing bowl; set aside.
Heat a 12-inch saute pan over medium-high heat. Add chickpeas, 1/4 cup Tomato Vinaigrette, and a pinch each of salt and pepper and toss to heat through, 1 to 2 minutes. Pour chickpeas over spinach mixture. Using a spatula, scrape any residual vinaigrette from pan into salad. Drizzle another 1 to 2 tablespoons of vinaigrette over salad and toss to coat well. Serve immediately.
Cook's note: If cooking all together, add warm tomato sauce from cooked mackerel and toss with red onion, bell pepper, black olives, salt, pepper, and chickpeas and pour over spinach to wilt.