Heat a medium saucepan with a lid over medium-high heat. Melt the coconut oil and add the scallion whites, garlic and serrano and cook, stirring frequently, until the garlic and scallions start to brown, 1 to 2 minutes. Sprinkle in the cumin, lime zest, 1 teaspoon salt and 1/2 teaspoon pepper. Add the rice and stir until all the beads of rice are coated. Add 2 to 3 cups water (according to the package directions) and stir. Bring to a simmer, then cover and reduce the heat to low. Cook until all the liquid is absorbed and the rice is tender, about 45 minutes. Fluff with a fork and serve with a spritz of lime and sliced scallion greens.