Heat tortillas as directed on package. While tortillas are heating, spray 10-inch nonstick skillet with cooking spray and heat over medium heat.
Cook mushrooms and onion in skillet about 5 minutes, stirring frequently, until onion is crisp-tender. Stir in beans and heat through. Stir in spinach. The heat will wilt the spinach leaves. Remove from heat.
Divide bean mixture among tortillas. Sprinkle with cheese. Fold one end of each tortilla up about 1 inch over filling and fold right and left sides over folded end, overlapping. Fold remaining end down.