Sprinkle both sides of fillets with seasoning. Coat a large nonstick skillet with cooking spray, and place over medium-high heat until hot. Add fish, and cook 3 minutes; remove skillet from heat.
Turn fish; top with spinach, tomato, and cheese. Return skillet to heat; cover and cook 3 to 4 minutes or until spinach is hot and fish flakes easily when tested with a fork.