Start by heating 2 tablespoons of oil in a large, heavy-bottomed pot over medium heat.
Add the sliced onions and sauté until they turn golden brown, about 10–12 minutes. Stir occasionally to prevent them from burning. This caramelization is key to the deep flavor of Sayadieh.
Once the onions are golden, add the minced garlic and chopped jalapeño. Sauté for another 2–3 minutes until the garlic is fragrant.
Combine the spice mix in a small bowl and set aside.
Season the white fish fillets with 1 teaspoon of the spice blend. Coat each fillet lightly with cornstarch, ensuring an even layer.
In a separate skillet, heat the remaining 2 tablespoons of oil over medium-high heat. Fry the fish fillets for 2–3 minutes per side until golden and slightly crispy outside. The goal is to create a flavorful crust while keeping the inside tender. Remove the fish from the skillet and set aside.
Return to the pot with the caramelized onions. Add the washed and drained basmati rice to the pot. Add all the remaining seasoning spices to the pot. Stir well to coat the onions and aromatics with the spices.
Pour in 3 cups of hot water, ensuring the rice is fully submerged. Bring the mixture to a gentle boil, then reduce the heat to a low simmer and cover the pot with a tight-fitting lid.
Let the rice cook for about 18–20 minutes or until tender and fluffy. Once the rice is cooked, gently fluff it with a fork.
Arrange the crispy fish fillets on top of the rice and sprinkle with toasted almond slivers, chopped parsley, and more caramelized onions.