Soak the rice in a bowl of hot water, about 5 minutes. Drain, rinse and shake dry.
Heat the vegetable oil in a large skillet over medium-high heat. Add the rice and toast, stirring, 8 to 10 minutes. Meanwhile, puree the garlic, onion and tomatoes in a blender. Add to the rice and cook until absorbed, about 3 minutes. Add 3 1/2 cups water, the jalapeno and a pinch of salt; cover and cook over medium heat until the rice is tender, about 10 minutes.
Remove the skillet from the heat. Uncover and place a clean towel over the rice, then re-cover and let stand 15 minutes. Fluff the rice with a fork; serve with the jalapeno, if desired.