1. 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.

2. 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.