1. Line a medium sieve (about 7 inches wide) with two layers of paper towels. Place sieve over a bowl. Stir yogurt in container for consistency before pouring into sieve. Adjust paper towels to remove any folds. Cover with plastic wrap and refrigerate 24 hours, until yogurt thickens.
2. Meanwhile, in a small saucepan, bring pineapple juice to a boil. Cook over high heat until reduced to scant 1 cup, 25 to 30 minutes. Remove from heat and let cool. Cover and refrigerate until cold.
3. When ready to serve, remove yogurt from refrigerator and place a plate over sieve, making sure paper towels are not covering yogurt. Turn plate and sieve over to unmold yogurt. Gently remove paper towels. With a knife, smooth yogurt on sides and top to make a flat ""cheesecake."" Garnish with strawberries and serve with pineapple sauce on the side.