Spicy Shrimp Fajitas with Grilled Pineapple Pico

Heat grill to medium-high; place a large cast-iron skillet on grates to preheat. Toss shrimp with adobo, zest, oil, and 1/2 teaspoon salt. Lightly brush onion and pineapple with oil; grill directly on grates, flipping once, until charred in spots, 6 to 8 minutes. Let cool slightly. Grill tortillas, flipping once, until charred, about 30 seconds; wrap in parchment-lined foil. Roughly chop pineapple and onion; toss with lime juice and cilantro. Season with salt and pepper.

Add shrimp and lime halves to skillet and cook, flipping once, until shrimp are pink and just cooked through, 3 minutes. Let lime halves cool slightly, then squeeze over shrimp; serve in tortillas with pineapple pico, cilantro sprigs, avocado, and sour cream.