In a medium saucepan, boil the rice in 4 cups of water for 25 minutes, or until just tender. Drain through a sieve and rinse with cold water to wash off the starch and cool the rice. Spread the rice in a flat metal pan and refrigerate for at least 30 minutes.
This is a dish that cooks quite quickly from this point on, so it's important to have all the ingredients prepared and ready at hand.
Remove the tough outside layer of the lemongrass and cut off the root end and the dry top. Start slicing from the root end and use only the most tender, bulb-like part of the stalk. Slice thinly and chop very fine so the flavor will be spread throughout. You should have about 1/4 cup, chopped.
Warm the oil in a large frying pan over medium-high heat. Saute the lemongrass, chiles, and garlic for 30 seconds to release the aromatic oils. Add the red pepper, celery, and ginger and stir-fry for another 30 seconds.
Add the chilled rice and cook until heated through, stirring occasionally to keep it form sticking. Add the pineapple, mint, and cilantro to the hot rice. Sprinkle the fish sauce, vinegar, and sesame oil over the top. (Vegetarian Option: Substitute tamari for the fish sauce.) Stir to mix and serve immediately.
Garnish with sprigs of mint and cilantro.