Preheat oven to 350 degrees.
Pour olive oil in a large skillet. Add onions, salt, pepper and half of beer. Simmer over medium heat until liquid evaporates. Stir and add remaining beer. Cook until onions are soft and liquid is absorbed, about 10 minutes. Remove from heat.
Heat tortillas in saute pan until warmed through.
Place tortillas on work surface. Drizzle mustard on top of center of tortilla. Top with a brat, an even amount of onions, and an even amount of cheese. Starting on one end of the tortilla, roll tortilla around the brat like a burrito, rolling tight. Roll tortilla into foil. Repeat process until all brats are wrapped. Place packages on baking sheet and place in oven. Bake 15 minutes or until warmed through.
Remove baking sheet from oven and keep brats in foil until ready to serve. Serve warm.
Recipe serves six and can be prepared in under one hour.
HINTS: Add peppers to onion mixture for added flavor or spice this recipe up with jalapeno slices. Gluten-free tortillas and other ingredients can easily be substituted in this recipe to make a gluten-free recipe. Variation to this recipe: Place six tooth picks into each wrapped brat and slice. Serve as brat bites.