15-Minute Skillet Pepper Steak with Colorful Bell Peppers

Ingredients

• 12 ounces top round beef, thinly sliced
• Kosher salt, to taste
• Freshly ground black pepper, to taste
• 2 tablespoons peanut oil, divided
• 1 tablespoon soy sauce
• 1 tablespoon rice wine vinegar
• 1½ teaspoons crushed red-pepper flakes
• 1 red bell pepper, thinly sliced
• 1 yellow bell pepper, thinly sliced
• 1 green bell pepper, thinly sliced
• 1 orange bell pepper, thinly sliced
• 3 garlic cloves, minced
• 1 bunch scallions, thinly sliced
• Sesame seeds, as needed for finishing