Preheat oven to 375 degrees.
Brush both sides of mackerel with olive oil. Place salt and white pepper in a small bowl and stir to mix well. Season both sides of fillets with seasoning.
In a large roasting pan, add warmed tomato sauce. Place fillets into sauce and transfer to oven. Cook until fish is just cooked through, 10 to 12 minutes. Remove from oven and transfer fillets to a serving plate.
Divide spinach and chickpea salad among 6 serving plates. Top with mackerel fillets, and drizzle with extra tomato vinaigrette as desired, and garnish with parsley. Serve immediately.