In a medium bowl, whisk together the achiote paste, pineapple juice, vinegar, minced chipotle, garlic, oregano, and cumin until smooth.
Add the shrimp to the marinade and toss to coat thoroughly; let sit for 10 to 15 minutes.
Heat the vegetable oil in a large skillet or griddle over medium-high heat.
Add the shrimp and diced pineapple to the skillet in a single layer.
Sear the shrimp for 2-3 minutes per side until opaque and slightly charred, and the pineapple is caramelized.
While shrimp is cooking, warm the corn tortillas in a separate dry skillet or over an open flame.
Assemble the tacos by placing 3-4 shrimp and pineapple chunks onto each tortilla.
Garnish with chopped cilantro, diced onion, and a squeeze of fresh lime juice.