1. In a medium-sized saucepan over high heat, bring 2 inches water to a boil. Drop in the asparagus and cover, and cook until just tender, approximately 5 minutes. Remove the asparagus and immediately rinse in cold water to stop the cooking process. Drain thoroughly.
2. In a small bowl, mash the avocado, lime juice, and garlic into a coarse puree. In another small bowl, stir together the rice and yogurt to mix well. Heat a large dry frying pan (not one with a nonstick surface) over medium heat. One at a time, heat the tortillas in the hot pan until softened, approximately 20 seconds per side.
3. Lay the tortillas flat on a clean work surface. Spread the avocado mixture equally among the tortillas. Top each with an equal amount of the rice mixture, asparagus, cilantro, and onion. Fold in both sides and the bottom of each tortilla up over the filling; then roll to close. If made in advance, cover with plastic wrap and refrigerate for up to 1 hour. Return to room temperature before serving.