1. Place the rice in a fine mesh sieve. Rinse under cold water, stirring rice until water runs clear (about 1 minute). Combine rice and 3/4 cup plus 1 tablespoon water in a small saucepan, and cover. Bring to a boil; cook 1 minute. Reduce heat, and simmer for 5 minutes. Increase heat to high, and cook for 30 seconds. Remove from heat. Let stand, covered, for 5 minutes.
2. Combine rice wine vinegar, mirin, 2 teaspoons sugar, and salt in a microwave-safe dish; microwave at HIGH for 30 seconds, stirring until sugar dissolves. Cool.
3. Place rice and 2 tablespoons vinegar mixture in a bowl; toss. Cover with a paper towel soaked in remaining vinegar mixture.
4. Combine remaining sugar and soy sauce in a small bowl. Heat a large skillet over medium-high heat. Coat pan with cooking spray. Add Spam to pan; cook 4 minutes on each side or until lightly browned. Add to soy mixture; toss. Let stand 5 minutes. Remove Spam from soy mixture; cut in half lengthwise. Reserve remaining soy mixture.
5. Cut off top quarter of each nori sheet along short end. Place 1 nori sheet, shiny side down, on a sushi mat covered with plastic wrap, with long end toward you. Pat about 3/4 cup rice mixture evenly over nori with moist hands, leaving a 1-inch border on 1 long end of nori. Arrange 2 Spam slices, 2 pineapple pieces, and 1 green onion piece along top third of rice-covered nori. Top with 1/4 teaspoon Sriracha and half of reserved soy mixture. Lift edge of nori closest to you; fold over filling. Lift bottom edge of sushi mat; roll toward top edge, pressing firmly on sushi roll. Continue rolling to top edge; press mat to seal sushi roll. Let rest, seam side down, 5 minutes. Slice roll crosswise into 10 pieces. Repeat procedure with the remaining rice, nori, Spam, pineapple, onion, Sriracha, and soy mixture.