Begin by heating 2 tablespoons of olive oil in a large skillet over medium heat. Allow the oil to shimmer, signaling it's ready for cooking, which takes about 2 minutes.

Add one finely chopped onion to the sizzling oil and sauté for about 5 minutes until it turns translucent and tender.

Incorporate 2 minced garlic cloves into the skillet, stirring for an additional minute until fragrant.

Sprinkle in 1 teaspoon of cayenne pepper, 1 teaspoon of ground cumin, and 1 teaspoon of paprika into the skillet. Stir the spices and cook for about 30 seconds.

Pour in 1 can (14.5 oz) of diced tomatoes and stir well to combine. Allow the mixture to come to a gentle simmer and cook for 10 minutes.

Gently place your firm white fish fillets into the simmering sauce, ensuring they are fully submerged. Cover and cook for 10 to 15 minutes until the fish flakes easily with a fork.

Taste the sauce after cooking, and add salt as needed.

Carefully transfer the fish and sauce to plates, garnishing with fresh cilantro and parsley.