Heat the oven to 200°F.

• 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.
• Set aside half the cumin-paprika spice blend for the vegetables.
• Rinse the shrimp, then drain on a paper-towel-lined plate and pat dry. Season lightly with salt and pepper.

In a large frying pan over medium-high heat, warm 2 tablespoons oil until hot but not smoking. Add the steak, half the cumin-paprika spice blend, and as much chili powder as you like and cook, stirring occasionally, until the steak is browned but not yet cooked through, 2 to 3 minutes. Transfer the steak to a medium bowl. Do not clean the pan.
In the same pan over medium-high heat, add the shrimp and cook, turning once, until firm and cooked through, 1 to 2 minutes per side. Transfer to the bowl with the steak and set aside.
While the steak and shrimp cook, heat the tortillas.

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. Be careful of the hot towel when unwrapping.
While the tortillas warm, prepare the vegetables.

• Remove the stems, ribs, and seeds from the red and green bell peppers. Thinly slice the bell peppers.
• Peel and thinly slice the yellow onion.
• Trim the ends from the squash; cut the squash in half crosswise, cut each half lengthwise into ¼-inch-thick slices, then cut the slices into ¼-inch-thick strips.

In the same pan used for the steak and shrimp, warm 1 tablespoon oil over medium heat until hot but not smoking. Add the bell peppers, onion, and remaining cumin-paprika spice blend and season with salt and pepper. Cook, stirring occasionally and scraping up any browned bits from the bottom of the pan, until the vegetables begin to soften, 4 to 5 minutes. Add the squash and cook, stirring occasionally, until all the vegetables are tender, 4 to 5 minutes longer.
While the vegetables cook, prepare the garnishes.

• Juice half the lime and set aside for finishing the steak and shrimp; cut half the lime into wedges.
• Trim the root end from the romaine; separate the romaine leaves.
• Coarsely chop the cilantro.

In another medium bowl, toss the cabbage with 1 teaspoon oil. Season to taste with salt and pepper.

When the vegetables are tender, add the steak, shrimp, and accumulated juices to the pan. Stir in the lime juice; cook until the steak and shrimp are warmed through, 1 to 2 minutes. Season to taste with salt and pepper.

Set out the tortillas, romaine leaves, steak and shrimp, cabbage, lime wedges, cilantro, pumpkin seeds, and yogurt. Invite everyone to assemble their own fajitas.