Combine the shallots, mustard, Sriracha and red wine vinegar, slowly whisk in the olive oil.
Combine the kale, radicchio or red cabbage, and carrots in a medium bowl. Toss with enough dressing to lightly coat the slaw just before serving. Season to taste with salt and pepper.
Heat 2 Tablespoons butter and 2 Tablespoons oil over medium-low heat. Add onions and sauté until golden brown.
Wrap the tortillas in foil and heat for 5-10 minutes in the oven.
Top each tortilla with braised beef, caramelized onion, and kale slaw. Garnish with avocado, cilantro, pepitas, jalapeno and cheese. Serve immediately.