Heat 2 tablespoons olive oil in a saucepan over medium-low heat. Add garlic and saute for 1 minute or until fragrant. Add grape tomatoes, salt and pepper and cook for 5 minutes, stirring occasionally. Then add chopped onions, crushed tomatoes and sliced olives; cook for a few more minutes or until onions softened, stirring occasionally. Taste for seasoning.
Meanwhile, wash the haddock fillets and pat dry. Coat filets lightly with olive oil. Season both sides with salt and black pepper. Place them into a baking dish.
Preheat oven to 420 degrees F. Place on the middle rack of the oven and bake until fish flakes easily with a fork, about 15 minutes (when a fish is properly cooked, the flesh should flake off in pieces when you touch it with a fork). Transfer to a serving plates and pour the Veracruz sauce over them. Serve immediately.