Heat oven to 450°F. Whisk eggs in medium bowl; whisk in milk. Add flour and salt; whisk well. (Some small lumps of flour will remain.) Whisk in butter.
Coat eight 6-ounce custard cups or ramekins with cooking spray; dust lightly with flour. (Note: Popovers may be made in muffin tins with 4-ounce cups. Coat 10 of the cups of a 12-cup muffin pan with cooking spray. Fill and bake as directed with custard cups.)
Pour batter into cups filling 1/3 full. Divide cheese evenly over batter. Pour remaining batter over cheese filling cups 2/3 full. Place cups on baking sheet; bake 15 minutes. Reduce oven temperature to 350°F; continue baking 20 to 25 minutes longer until puffed and deep golden brown (do not open oven during baking time).
Immediately remove popovers from baking cups to serving plates.
While popovers are baking, combine greens, cucumber, cheese and dressing in large bowl. Toss well and transfer to 4 serving plates. Top salads with salmon and dill. Serve with warm popovers.