Prepare a charcoal or gas grill to medium-high heat. Juice 1–2 limes to get ¼ cup juice; cut remaining limes into wedges for serving.
Add shrimp to a medium bowl with 2 tablespoons lime juice, 3 tablespoons vegetable oil, 1 teaspoon coriander, 1 teaspoon smoked paprika, 1 teaspoon kosher salt, a few turns black pepper, and ¼ teaspoon cayenne. Toss to coat then thread shrimp onto skewers; refrigerate until ready to grill.
Cut red onion crosswise into rounds. Finely dice ¼ cup of red onion and transfer to a small bowl. To diced onion, add remaining 2 tablespoons lime juice, 2 tablespoons olive oil, 1 minced serrano, 1 small grated clove garlic, and ½ teaspoon kosher salt; stir to combine and set aside.
Place remaining red onion rounds on a sheet pan or platter and add scallions, quartered peppers, and sliced pineapple. Drizzle with remaining 2 tablespoons vegetable oil and season with 1 teaspoon kosher salt and a few turns black pepper.
Place scallions, red onion, peppers, and pineapple on grill grate (in that order). By the time the last piece of pineapple has been added to grill, you’ll want to flip the scallions. Cook for another minute until charred then remove and transfer back to sheet pan (2–3 minutes total for scallions). Continue grilling red onion, peppers, and pineapple until charred and tender, turning occasionally, 10–15 minutes total. Transfer to sheet pan.
Add shrimp skewers to grill and cook until shrimp is lightly charred and just cooked through, turning once, 4–5 minutes depending on size. Meanwhile, add tortillas to a cooler section (usually outside edge) of grill and cook until puffed up and lightly brown, 1–2 minutes. Wrap tortillas in a towel to keep warm and pliable.
Finely dice ¾ cup of charred pineapple and add to bowl with diced red onion and serrano. Add ¼ cup cilantro and stir to combine.
Thinly slice remaining pineapple and peppers and cut scallions into 1-inch pieces.
Remove shrimp from skewers and arrange on a large platter with charred vegetables, pineapple, tortillas, avocado, and pineapple salsa.
Serve family-style with lime wedges and hot sauce.