Season the steak with salt and pepper and let it sit while the vegetables are prepared.
Heat oil in a skillet, cook the peppers and onion until softened and lightly charred, then transfer them to a plate.
Cook the steak in the hot skillet until browned and medium-rare to medium, then rest it for five minutes.
Slice the steak thinly across the grain and warm the flatbreads.
Spread pesto over each flatbread and top with peppers, onion, and sliced steak. Serve immediately.
Notes
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