Bring water to a boil in a small saucepan over high heat. Stir in barley, reduce heat, cover tightly, and simmer 10 -12 minutes or until tender. Remove from heat and let stand 5 minutes.
Meanwhile, heat 1/2 tbsp (7 mL) canola oil in a large nonstick skillet over medium-high heat. Tilt skillet to coat bottom evenly; add onions, and cook 6 minutes or until richly browned, stirring frequently. Add mushrooms and cook 4 minutes or until tender, using two utensils to toss. Add garlic and cook 30 seconds, stirring constantly.
Remove from heat. Add spinach, oregano and undrained barley. Toss well to blend. Drizzle remaining 1 tbsp (15 mL) canola oil evenly over all and toss gently until just coated.