For the steak wrap: Combine the beer, salt, cumin, paprika, black pepper and red pepper flakes in a large bowl. Add the cubed steak, cover with plastic and let marinate for at least 1 hour or as long as overnight.
Preheat a grill or grill pan to medium-high heat.
Remove the steak cubes to a paper-towel-lined plate and pat dry. Transfer the steak to the grill and cook until done and nicely grill-marked on all sides, about 1 1/2 minutes per side. Remove to a plate and let cool for 10 minutes.
Lay a tortilla on a cutting board. Arrange a quarter of the julienned peppers on the bottom third of the tortilla. Top the peppers with a quarter of the watercress, then with a quarter of the steak. Drizzle with a couple tablespoons of the cucumber-yogurt sauce. Fold the bottom third of the tortilla up over the filling. Fold in the sides about a third of the way toward the center. Roll up the tortilla from the bottom until the filling is completely wrapped. Repeat with the remaining tortillas. If youre not serving immediately, cover the finished wraps in parchment or plastic and store in fridge until ready to serve.