Place a rack in the upper-middle position and preheat the oven to 425°F. Line a large rimmed sheet pan with foil or parchment for easy cleanup, then brush or spray lightly with oil.

Toss the bell peppers and red onion with 2 tablespoons of the olive oil and 1 tablespoon of the fajita seasoning. Spread in a single layer on the sheet pan — give them room; crowding steams instead of roasts. Roast for 10 minutes, until the peppers are starting to soften and char at the edges. The peppers need this head start because the shrimp cook much faster.

While the vegetables roast, pat the shrimp very dry with paper towels (dry shrimp sear and roast better). Toss with the remaining 1 tablespoon olive oil, the remaining 2 tablespoons fajita seasoning, the lime juice, and the salt.

Remove the sheet pan from the oven. Push the vegetables to make room, then arrange the shrimp in a single layer over and around them. Return to the oven and roast 8–10 minutes, until the shrimp are pink, opaque, and curled into loose C-shapes. Don’t walk away at the end — shrimp go from perfect to rubbery fast.

While the shrimp finish, warm the tortillas: wrap the stack in a damp paper towel and microwave 30–45 seconds, or char them directly over a gas burner for a few seconds per side.

Shower the pan with cilantro and a squeeze of fresh lime. Pile shrimp and vegetables into warm tortillas and pass the sour cream, guacamole, and pico de gallo. Serve straight from the sheet pan — it’s part of the fun.