Heat the oven to 355°F (180°C) and position a rack in the lower third.

Layer the potato and sweet potato slices in the bottom of a 9x13-inch/23x33 cm baking dish, overlapping them slightly. Arrange the salmon fillets over the top. Scatter the cherry tomatoes and garlic cloves around and over the fish.

In a measuring cup or small bowl, combine the hot water with the fish seasoning, hawaij, a generous pinch of salt, and several grinds of black pepper. Stir until the spices dissolve. Pour the mixture evenly over the dish.

Sprinkle the fresh herbs over the salmon and drizzle everything with olive oil. Cover the dish tightly with foil and bake on the lower rack for 40 minutes, or until the vegetables are tender and the salmon is just cooked through.

Remove the foil and increase the oven temperature to 400°F (200°C). Continue baking for 10 minutes, until the tomatoes blister and the top is lightly browned. Serve hot, spooning the flavorful pan juices over each serving.