Preheat oven to 425 degrees F. Peel sweet potatoes and cut into strips about 3" long and 3/4" thick.
In a small bowl, mix together herbs and spices. On a rimmed baking sheet, toss together cut sweet potatoes, 3 tablespoons of the olive oil, and herbs and spice mixture.
Spread out sweet potatoes in a single layer. Roast 20 minutes, turning every ten minutes. After 20 minutes, rub remaining 1 1/2 tablespoons olive oil on the fish fillets, and season with salt and pepper. Move sweet potatoes around making rom for the fish at one end of pan. Cook for 15-20 more minutes until fish is cooked and sweet potatoes are tender and lightly browned.