Heat grill to medium heat. Cook and stir onions in hot olive oil in large non-stick skillet on medium high heat for 5 minutes or until onions are golden brown; cover and simmer on low heat for 10 minutes.
While you are cooking the onions, bring beer to a boil in medium saucepan. Add bratwurst; cook for 5 minutes. Drain. Put brats on grill and grill 4-5 minutes until heated through and browned, turning occasionally.
Stir steak sauce into onions. Top each tortilla with a cheese slice, onions and a bratwurst. Roll up and serve.