Soak 24 bamboo skewers, 8 to 10 inches long in water for 30 minutes or longer if convenient.
Prepare a grill 45 minutes before you are ready to cook or preheat the broiler 15 minutes before cooking.
Thread 3 pieces of fish, alternating with 2 slices of yellow pepper and 2 of red pepper, on parallel skewers about 3/4 inch apart so the brochettes will be easier to turn and the food will stay in place while cooking.
Brush with olive oil and season with salt and pepper. Set aside.
In a 2-quart non-reactive saucepan, cook the orange juice and scallions over medium heat until the liquid is reduced to half the amount, about 25 minutes.
Lower the heat to very low and whisk in the butter 1 tablespoon at a time only until melted. Stir in the cumin, hot pepper flakes, and additional salt if you wish. Keep warm over very low heat.
When the grill or broiler is ready, grill the brochettes 4 inches from the heat, turning occasionally and basting with some of the orange butter sauce, for 10 to 12 minutes until the fish is opaque and slightly brown on the outside.
Stir the tomatoes and cilantro into the remaining sauce. Place the brochettes on serving plates and spoon some of the sauce over each brochette.
