Mix the cumin, chili powder, oregano, paprika, black pepper, red pepper flakes (if using) and half the salt together. Place fish in a small dish and evenly coat each side with the seasoning. Set aside.
Heat 1 teaspoon of olive oil in a saute pan over medium-high heat. Once the oil is hot, add the red bell pepper, white part of the green onion, garlic and corn to the pan. Stir for about 3 minutes.
Add the vinegar and cook until it no longer smells acidic. Then stir in the tomatoes and remaining salt. Cook until the relish starts to thicken. Add the lime juice, honey, cilantro and green parts of the onions to the pan. Transfer to a bowl and cover to keep warm.
Wipe out the pan and heat remaining olive oil over medium-high heat. Add the fish and cook until golden brown on the underside. Flip the fish over using a spatula and cook until the second side browns.
If your fish is thick and needs to be cooked further, finish it in the oven at 350°. Divide the fish among the corn tortillas and top with corn relish.