Heat oil in a Dutch oven over medium-high heat. Add ginger and garlic; sauté 90 seconds. Add curry; cook 15 seconds, stirring constantly. Add mirin; cook until liquid is reduced to 1/2 cup (about 4 minutes). Add squash, broth, and celeriac; bring to a boil. Reduce heat, and simmer 15 minutes or until tender.
Place one-fourth of squash mixture in a blender; process until smooth. Pour pureed squash mixture through a sieve over a large bowl, reserving liquid; discard solids. Repeat procedure in 3 more batches with remaining squash mixture. Stir in orange juice concentrate, Sriracha, and salt. Dollop 1 tablespoon yogurt over each serving; sprinkle with parsley.