In a small, airtight container, combine shallot, vinegar, oil, water, mustard, honey, 1/4 tsp salt and 1/8 tsp pepper; shake well.
Coat a rimmed baking sheet with cooking spray; add squash in an even layer. Coat squash with cooking spray and sprinkle with 1/4 tsp salt and 1/8 tsp pepper; roast until soft and lightly browned, 15-20 minutes.
While squash roasts, coat a grill pan with cooking spray; heat over medium-high heat. Sprinkle steak with remaining salt and pepper (and season with dried oregano and granulated garlic, if desired); cook, turning once, to desired degree of doneness (about 6 minutes per side for rare). Remove from heat; let rest for 5 minutes before slicing thinly.
Place 1/2 c barley in each of four bowls. Top each with 1 c arugula, 1/4 of squash and 2 oz steak; drizzle each with 2 Tbsp dressing. Sprinkle each with 1 Tbsp goat cheese; serve.