Combine 1 tablespoon of the lemon oil, garlic paste, zest, fennel seeds, and pepper in a small bowl. Rub the mixture over the pork tenderloins and let stand at room temperature, covered, for 30 minutes. Meanwhile, preheat the oven to 425 degrees F.
Heat the remaining 2 tablespoons lemon oil in a large skillet over medium heat. Brown the pork tenderloins, about 5 minutes total. Transfer to a baking pan and roast the pork for about 15 to 20 minutes, or until an inserted instant read thermometer reads 150 degrees F, about 15 to 20 minutes, for medium, or to desired doneness. Remove the pork to a platter and let sit for 10 minutes before cutting into thin slices.
Variation: If you'd like to serve fresh fennel alongside the pork, after browning the pork, add the fennel to the same skillet. Cook the fennel, stirring frequently, over medium heat until it begins to brown, about 10 minutes. Add a minced garlic clove, a teaspoon of sugar and cook, stirring, for 1 minute. Add 3/4 cup cool water, bring to a boil and simmer until the liquid is all evaporated and the fennel is fork-tender, about 5 minutes. Stir in 1 tablespoon of fresh lemon juice and season with salt and pepper.
Place the oil and the zest in a glass jar. Let stand at room temperature for at least 2 weeks, shaking occasionally.
Pour the oil through a strainer and discard the zest. Transfer to a jar and store, tightly covered, at in refrigerator.