Sprinkle the steak all over with 1/4 teaspoon salt. Heat the olive oil in a large skillet over medium-high heat. Add the steak and sear until browned, about 2 minutes per side. Transfer to a plate.

Add the garlic to the skillet. Once it sizzles, add the onion and bell peppers and cook, stirring occasionally, until they soften slightly, about 4 minutes. Add the pepperoncini, tomatoes, oregano, red pepper flakes and 3/4 cup water and stir to combine. Bring to a rapid simmer, then nestle the steak in the sauce and simmer, turning once, until medium rare, about 7 minutes. Transfer the steak to a cutting board and let rest about 5 minutes. Continue simmering the sauce until thickened, about 3 more minutes.

Thinly slice the steak against the grain and divide among plates. Top with the sauce and parsley. Serve with focaccia.