Step 1Cut each pepper half in half crosswise, then lengthwise in strips of about 2 inches by 1/4 inch; you will have a total of about 2 cups pepper strips.
Step 2Heat 2 tablespoons oil in a sauté pan or deep, medium-size skillet (about 9 1/2 inches wide) over medium-low heat. Add the chopped onion and cook to soften it slightly, 2 minutes. Add the pepper strips and a pinch of salt and cook until the peppers are nearly tender, about 10 minutes; do not brown the onions. Remove the mixture from pan and set aside. Wipe the pan if necessary.
Step 3To peel the tomatoes: In a medium saucepan, boil enough water to generously cover the tomatoes over high heat. Prepare a bowl with enough ice water to cover the tomatoes. Core the tomatoes and slit the skin at the bottom of each tomato in an X. Put the tomatoes in the boiling water and boil just until the skins start to pull away from the X, about 30 seconds. Transfer the tomatoes to the bowl of ice water. Remove the tomatoes from the cold water promptly and pull off the peel with the aid of a paring knife. Halve the tomatoes and squeeze out their juice and seeds, reserving the juice. Chop the tomatoes very fine; you should have about 1 cup. Strain the tomato juice.
Step 4Cut each tilapia fillet in half lengthwise along the center line.
Step 5Heat 1 tablespoon olive oil in the sauté pan over medium-low heat. Add 1 1/2 teaspoons of the minced garlic and cook until it is fragrant, about 10 seconds. Add the tomatoes, saffron, turmeric, paprika, oregano and a pinch of salt and pepper. Cover and cook over medium-low heat, stirring occasionally, until the tomatoes soften, about 5 minutes. Add 1 cup water and bring to a boil. Cover and simmer over low heat for 3 minutes to blend flavors.
Step 6Add about half the tilapia fillets, or enough to make one layer, to the sauce. Sprinkle each fillet lightly with salt and pepper. Return the sauce to a simmer over high heat. Cover and cook over medium-low heat until the fish becomes opaque in its thickest part, about 4 minutes for thinner pieces or about 5 minutes for thicker ones; check with the point of a sharp knife. Using a fish spatula or slotted spatula, transfer each piece gently to a plate. Repeat with the remaining tilapia fillets. .
Step 7Add the onion-pepper mixture to the sauce and bring it to a simmer. Cover and cook over medium-low heat, stirring occasionally, until the peppers are tender, about 5 minutes. If the pan becomes dry during simmering, add 2 or 3 tablespoons water, 1 tablespoon at a time. Add the remaining 1 1/2 teaspoons garlic, stir and remove from the heat.
Step 8Drain any liquid from the plate of tilapia into the sauce. If the sauce is too thick, add 2 to 4 tablespoons of the reserved tomato juice. Add cayenne pepper if desired and 1 tablespoon olive oil. Stir in 2 tablespoons cilantro. Taste and adjust seasoning.
Step 9Put the tilapia on a serving platter or on plates and top each piece with some of the pepper sauce. Sprinkle with the remaining cilantro. Serve at room temperature.