Heat the oven to 200ºF.

• Remove the stems, seeds, and ribs from the red and yellow bell peppers; cut the peppers into ¼-inch-wide strips.
• Trim the root ends from the scallions; cut the scallions into 1-inch lengths.
• If using the jalapeño, remove the stem, seeds, and ribs; thinly slice the jalapeño. Wash your hands after handling.

In a large frying pan, warm 2 to 3 tablespoons oil over medium-high heat until hot but not smoking. Add the bell peppers, scallions, and as much jalapeño as you like. Season with salt and cook, stirring occasionally, until softened and slightly caramelized, 3 to 5 minutes. Transfer to a plate. Do not wipe out the pan.
While the vegetables cook, warm the tortillas, if using.

Lay a damp kitchen towel on a sheet pan. Arrange the tortillas on one end of the towel, overlapping them slightly; cover them with the other end of the towel. Heat in the oven until warmed through and just pliable, 10 to 12 minutes. Remove from the oven and let stand, still covered, until ready to use.
While the tortillas warm, prepare the salsa and cook the steak.

• Peel the cucumber, if desired, and trim off the ends; cut the cucumber in half lengthwise, then crosswise into ¼-inch-thick half-moons.
• Trim the ends from the radishes. Cut them in half, then cut the halves into thin half-moons.
• Coarsely chop the cilantro.
• Juice 1 lime.
• Cut 1 lime into wedges for garnish.
• Trim the root end from the romaine heart.
• Separate the romaine leaves.

In a medium bowl, stir together the cucumber, radishes, cilantro, lime juice, and 1½ teaspoons oil. Season to taste with salt.

• Cut a small corner from the steak packaging and drain off any excess liquid. Transfer to a plate; pat dry with a paper towel. Season generously with salt and pepper.
• In a medium bowl, combine the steak with the steak fajita spice blend and tomato paste and stir well to coat; season generously with salt.

In the same frying pan used for the vegetables over medium-high heat, warm 1 tablespoon oil until hot but not smoking. Add the steak and cook, stirring occasionally, until browned but not yet cooked through, 2 to 4 minutes. Transfer the steak to a plate.

Set out the tortillas, romaine leaves, steak, peppers, salsa, yogurt, and lime wedges. Invite everyone to assemble their own fajitas.

Chef’s tip: If you use the tortillas, you can also warm them on the stovetop directly over a flame, or in a dry frying pan over medium heat, until just pliable and warmed through, about 30 seconds per side. Transfer to a clean kitchen towel, cover, and keep warm.

Kids can!

• Arrange the tortillas for warming in the oven.
• Juice the lime.
• Stir together the salsa ingredients.
• Separate the romaine leaves.
• Set out the fajitas fixings.