Preheat the oven to 500°. Place the pork in a roasting pan, rub with the olive oil and season with salt. Roast for 10 minutes, then turn over and roast for another 10 minutes. Remove the tenderloins from the oven and let rest for 10 minutes.
Meanwhile, in a large skillet, melt 2 tablespoons butter over medium-low heat, add the onions and cook, stirring occasionally, until softened, 10 to 15 minutes. Stir in the cumin and half the orange juice; cook for 5 minutes. Stir in the honey and cook for 5 minutes more. Let cool.
In a medium saucepan, bring 1 1/2 cups salted water to a boil, stir in the rice, cover, lower the heat and simmer for 15 minutes. Remove from the heat and let rest for 5 minutes. Stir in the remaining 1 tablespoon butter, then the remaining orange juice and the cilantro. Season with salt.
Spoon the rice onto plates and sprinkle with the grated orange peel. Cut the pork diagonally into 1/2-inch slices and place on the rice. Spoon the onion marmalade over the pork and serve extra on the side.