Arrange bell peppers in a single layer on a foil-lined jelly-roll pan; lightly coat peppers with cooking spray. Broil peppers 4 minutes on each side or until blackened. Cool slightly; discard stems. Cut peppers into strips.
Combine chipotle, paprika, and salt; rub spice mixture evenly over steak. Place steak on a broiler pan coated with cooking spray; broil 5 minutes on each side or until desired degree of doneness. Let steak stand 10 minutes; thinly slice steak across the grain. Combine mayonnaise and next 4 ingredients; stir well.
Working with 1 tortilla at a time, heat tortillas over medium-high heat, directly on the eye of a burner, for about 15 seconds on each side or until lightly charred. Place 2 tortillas on each of 4 plates. Divide steak evenly among tortillas; top each taco with 1/4 cup sweet peppers, 1 tablespoon salsa, 1 tablespoon cheese, and 1 1/2 teaspoons mayonnaise mixture.