Preheat oven to 400°.
To prepare salmon, combine first 6 ingredients; rub spice mixture evenly over fish. Place onion in an 11 x 7-inch baking dish coated with cooking spray. Place fish on top of onion; bake at 400° for 20 minutes or until fish flakes easily when tested with a fork or until desired degree of doneness.
To prepare spinach, heat oil in a large nonstick skillet over medium heat. Add garlic to pan; cook 1 minute. Add half of spinach; cook for 1 minute, stirring frequently. Add remaining spinach; cook 4 minutes or until wilted, stirring frequently. Sprinkle spinach mixture with rind and 1/4 teaspoon salt. Stir in juice; remove from heat.
Place salmon on a platter. Arrange onions and spinach evenly around salmon. Sprinkle salmon with chopped fresh cilantro. Serve with lemon wedges, if desired.
Wine note: This salmon has lots of rich, piquant flavor and needs a wine that won't be intimidated by such bold spices as cumin, coriander, and cinnamon. Riesling's fruitiness offsets the spices while its clean, pure freshness is exactly the right counterpoint to the rich salmon. Washington State makes some of the best rieslings in the country. Try the new one from Long Shadows Vintners called Poet's Leap. The 2005 is $20. If you need a kosher wine, visit Wine-Searcher.com. --Karen MacNeil