Season the steak with salt and thinly slice.
Preheat the grill (or a heavy skillet over medium-high heat), add a drizzle of oil (if you’re using a skillet) and cook the steak for a few minutes, tossing with tongs, until just cooked through.
Set aside and cook the pepper in the same skillet for 2-3 minutes, until tender-crisp.
Meanwhile, stir together the yogurt, lemon juice, garlic and a pinch of salt.
Grill or warm the flatbreads and serve the steak and peppers on them, drizzled with garlic-lemon yogurt, to wrap and eat.