Arrange salmon in a dish just big enough to hold the fillet; pour orange juice mixture over salmon. Marinate in the refrigerator for 30 minutes, turning salmon once to distribute flavours. Discard marinade.
Grill salmon skin side up, over medium heat for 5 to 7 minutes; turn and cook for another 5 to 7 minutes, until fish flakes easily.
Just before salmon is done, sauté spinach in 1 tsp canola oil in a non-stick skillet just until wilted. Season with lemon juice and pepper.
Spoon spinach onto heated plates. Top with salmon. Sprinkle with grated orange peel.